Physics Grade -10 (Science - New Course )

 


                  Physics
Unit       -              Topics
7    -         Force and Motion
8     -       Pressure
9     -       Heat
10   -       Wave
11   -       Electricity And Magnetism

Unit -  7        Mation and Force
Force :-A physical quantity which change the state of an object is called force. Its S.I. unit (N).  It is a vector quantity. Eg. Pulling force, Gravitational force etc.
Force(F)=Mass(m)×acceleration(a)   or  mass(m)×acceleration due to gravity (g)
Gravitation or Gravitational force:-The force of attraction between any two heavenly bodies is called gravitational
force. Its S. I. unit is Newton(N).
              Gravitational force(F)=Gm1m2/d2
Where m1=mass of 1st body ,m2=mass of 2nd body ,d=distance between two heavenly bodies.

Factors affecting gravitational force:-
1)Mass of 2 heavenly bodies
 2)Distance between two object from their center

Newton’s law of gravitation:-The force of attraction between two heavenly is directly proportional to the product of masses ,and inversely proportional to the square of distance from their center is known as Newton’s law of gravitation. 

  F∞m1m2                   ―                i
  F∞1/d2                ―                ii     

This law is applicable for all objects and every where in this universe ie terrestrial or celestial so, it is called Newton’s universal  Law of gravitation.

Consequences  or effects of gravitational force :-
  i) Existence of solar system and galaxies.
  ii)Revolution of planets around the sun.

 iii)Revolution of moon around the earth and other  natural and artificial satellites around their respective    planets.
 iv)Formation of tides in the ocean and sea Ievel  i.e.gravitational  force of moon. 

Application of gravitational force or Newton’s law of gravitation:-
i)    It help to determine the mass of earth and other  
heavenly bodies.
ii)   It help to calculate the distance between any two heavenly bodies.ie earth and moon.
iii).  It help to discovering new planets stars and other heavenly bodies.

 Prove that  F=Gm1m2/d2
                                             
  
 
Suppose, Mass of 1st body=m1
Mass of 2nd body =m2
Distance between two heavenly bodies from their center=d
If force of attraction between them=F
Now, according  to Newton’s law of gravitation.
F∞m1m2
F∞1/d2
Combining   eqn ( i) and  eqn (ii)
F∞Gm1m2/d2
Or, F=Gm1m2/d2    (where G is universal gravitational constant)
؞F=Gm1m2/d2   Proved
Combining   eqn ( i) and  eqn (ii)
F∞Gm1m2/d2
Or, F=Gm1m2/d2    (where G is universal gravitational constant)
؞F=Gm1m2/d2   Proved


 Gravity:-The force by which a heavenly body ie. Earth attract another body towards the center of its is called gravity. Its S.I. unit is Newton’s (N) ie. The force of attraction of earth on us.
               Gravity(F)  =  GMm/R2
Where ,M=Mass of heavenly body ,m=Mass of object lying on the surface of heavenly body, R=Radius of heavenly body.
Consequences  or effects of gravity:-
i)Presence of weight in every body can stand and walk on the surface of earth.
iv)The earth is surrounded by the atmosphere .
v)Acceleration is produced in freely falling object.


Prove that  g∞1/R2

Suppose ,Mass of an object lying on the surface of  earth=m
Mass of earth =M
Radius of earth=R
According to Newton’s law gravitation
F=GMm/R2              ㅡ     i
According to Newton’s second  law motion ,the force of gravity acting on the body.
F=mg                   ㅡ      ii
Equating the relation of eqn(i) and eqn (ii)
mg=GMm/R2
or,  g=GM/R2
or, g∞1/R2       (where G and M are constant)
؞g∞1/R2  Proved.
(Thus, acceleration due to gravity is inversely proportional to square of distance from the center of heavenly bodies)


Acceleration due gravity:-

The acceleration produced in freely falling object towards the surface of earth due to influence of gravity is called acceleration due to gravity. Its symbol is g and S.I. unit is m/s2.The value of g at poles of earth is 9.83m/s,2 equatorial region is 9.78m/s2 and centre of earth is 0m/s2.It acts towards the centre of earth or the direction of acceleration due gravity is always downwards I.e. towards the centre of heavenly bodies.
          Acceleration due to gravity(g)=GM/R2
Where, M=mass of heavenly bodies ie. Earth, m=mass of object lying on the surface of heavenly bodies ie. Earth.
Note:- The value of acceleration due to gravity of earth=9.8m/s2,Moon =1.6m/s2,Jupitor =25m/s2


Variation of g with height from the surface of earth :-

Consider the mass of the earth be M,
and radius R respectively. The acceleration   
due to gravity on the surface of earth is given  byg=GM/R2        ―      i )
 Now ,g’ be the acceleration due gravity                                                                  at height h from the surface of earth,we get  Earth 
                   g’=GM/(R+h)2       ─       ii )
      Dividing eqn(ii)by eqn(i)                   g’/g=GM/(R+h)2 =R2/GM
or g’/g=(R/R+h)2
     or g’=(R/R+h)2×g   
      ∴       g’<g                              (since (R/R+h)2<1)
Therefore the value of acceleration due to gravity goes on decreasing with increasing the height from the surface of the earth.  
Ans : It means that earth produce an acceleration of 9.8m/s2on freely falling object towards the surface of earth under the influence  of gravity.
Q.2)If an iron ball and feather are dropped simultaneously in vacuum which one will strike the ground first and why ?
Ans: Both iron ball and feather will reach the ground simultaneously because if there is no  external resistance .  Q.1)What do you mean by the statement the acceleration due to gravity of  earth is 9.8m/s2?


Universal gravitational constant(G):-   

The gravitational force between two unit of masses kept at 1metre distance is called universal gravitational constant(G).Its SI unit is Nm2/kg2and value is  6.67x10-11 Nm2/kg2.It is constant all over universe .It is a scalar quantity.


The experiment was first performed by Robert Boyl in 1590 to verify idea of   Galileo when all object is    dropped from same height at same time strike ground together.

In the experiment coin and feather are kept in a long glass tube and tube is quickly inverted then ,the air inside the tube is removed with vacuum pump and same experiment is repeated. when air inside the tube coin reach other end faster than feather but when there is no air or vacuum both coin and father reach the other end at the same time.


Conclusion of coin and feather experiment:

Coin and feather experiment conform that if there is no external resistance all bodies falls towards the surface of earth with same acceleration.

Q 1)A feather and coin falls together on the surface of moon why?
Ans. There is no air on the surface of moon therefore a feather and coin falls together on the surface of moon due to same acceleration due gravity in all object.

2.)Why is the value of g differ from place to place on the surface of earth?
Ans. The value g depend on radius of the earth, and radius of earth is differ from place to place on the surface of earth. Therefore the value of g is differ from place to place on surface earth ,because we know that g∞1/R2

3.)Why is the value of g is more at polar region than that of equatorial region on the surface of earth ?
Ans.)The value of g depend on the radius of earth and radius of earth is more at equatorial region than that polar region, therefore the value of g is more at polar region than that of equatorial on the surface earth, because we know that g∞1/R2.

4.)Why is the value of g is more at terai region than that of mountains or Himalaya region?
5.)Why is the weight of object is differ from place to place on surface of earth?
Ans.)The weight of an object depend on the value of g and value g depend on the radius of earth, and the radius of earth is differ from place to place on the surface of earth, therefore the weight of an object is differ from place to place on the surface of earth.

6.)Why is weight of object more at Terai region that of mountains region ?
Ans. The weight of object depend on value g and value g depend on radius  earth and of earth is more at mountains region than that of Terai .Therefore the weight object is more at Terai region than that of mountains region, because we know that w∞g∞1/R2.

7.)Why is weight of object more at polar region than that equatorial region on the surface of the earth?
Ans. The weight of the object depend on the value of g and more at equatorial region than that of polar region of earth of earth. Therefore ,the weight of object is more at polar region than that of equatorial region of earth ,because we know that w∞g∞1/R2.

 

Differences between mass and weight.
 

Mass

Weight

1.The total amount of matter contained in abody is called mass.

2.It is a fundamental quantity.

3.Its SI unit is Kg.

4.It is measured by beam balance.

5.It is a scalar quantity.

6.It is constant all over the universe. Mass(m)=W/g

1.The of amount of force gravity acting on a body is called weight.

2.It is a derived quantity.

3.Its SI unit is N.

4.It is measurement by spring balance.

5.It is a vector quantity.

6.It is variable place to place.

Weight(W)=mg


Free fall:-If an object is falling without external resistance is called free fall.
                                Or
If an object is falling with acceleration due to gravity in the absence of air is called free fall .Eg .body falling in vacuum ,body falling on the surface of moon ,body falling in the acceleration due to gravity .In every free fall there is weightlessness.
 
Equation of motion for Free fall :
For Motion                                            For Free fall
i)v = u+at                                          i)v = u+gt
ii)v2   =   u2 + 2as                                         ii)v2  =u2 +2gs
iii) s  = ut + ½ at2                               iii) s = ut + 1/2gt2
 
1.)The fall of a parachute toward the earth surface is not a free fall” ,justify this statement .
Ans. A body is said to have free fall, if it does not experience any kind of resistance during falling .but when parachute falls  towards  the surface of earth, it experience up thrust of air from opposite direction ,therefore falls of parachute is not free fall.
 2.) How does parachute fall ?explain.
Ans. When parachutist jump at first speed of parachute goes on increasing due to effect of gravity same time parachute open due to up thrust of air then after certain time magnitude of gravity and up thrust of air from opposite direction become equal  and velocity remains constant ,acceleration will be zero so parachute falls towards earth slowly  with low velocity.
3.)A parachutist is not hurt jumps from at great height ,why?
Ans. When parachutist  jumps from at great height due its large volume experience equal magnitude of up thrust of air from opposite direction to the acting on the parachute. Therefore falling slowly with low velocity towards the surface of earth and does not get any hurt.
4.)What is difference in the falls of parachute on the surface of earth and moon.
Ans. On the surface of earth parachute does not freely falls due to presence of air ,but on the surface of moon object falls freely due to absence of atmosphere.
5.)Weight of object is less in mine of coal ,why ?
Ans. The weight object depends on the value of g and value of g depends on the depth from the surface of earth ,while going downward in mine depth of earth increases ,value of g decrease so the weight of an object decreases because we know that weight∞g∞1/depth
6.)What change is seen on acceleration due gravity as we  move towards the centre of earth.
Ans. When we move towards the centre of the vale of g goes on decreasing and centre of earth value g is zero. because we know that g∞1/depth of the surface of earth
7.)The probability of hurt is more when a person jumps from a significant height ,why?
Ans. If person jumps from a certain height ,his acceleration goes on increasing towards the earth surface and force is directly proportional to acceleration due to gravity so the more acceleration more will strike force .Therefore the of getting     hurt is more when a person jumps from a significant height .

Numerimcal  problems
F=Gm1m2/d2                ―     i)
F=GMm/R2                      ㄧ   ii)
g=GM/R2                          ㅡ    IIi)
g=GM/(R+h)2                  ㄧ   iv)
W=mg                         ㅡ      v)
g’=(R/R+h)2×g            ㄧ      vi)
h=ut+1/2gt2                     ㅡ     Vii)
v2=u2+2gs                   ㅡ      viii)
Wt. lift on the surface of earth=wt lift on the surface of moon   
WE=WM          or        mgE=mgm              - ix)
Jump on the earth surface(h)×gE=     Weight lift on the moon surface(h)×gM    -  x)

1.)What is gravitational force when the distance the object is made double ?
       From Newton’s law of gravitation
             F=Gm1m2/d2           ㅡ   i)
  According to question.
  M1=m1,   m2=m2       ,d=2d
  According to Newton’s law of gravitation
F’ =Gm1m2/d2
0r F’ =Gm1m2/(2d)2
0r F’= Gm1m2/4d2
Or F’= 1(Gm1m2)/4d2
From equn(i)
F’=1F/4
؞The force will be 1F/4 the initial force.  
2.)What change in gravitational force is seen when masses and made double and distance is halved .
From Newton’s law of gravitation
 F=Gm1m2/d2            ㅡ    i)
According to question
M1=2m1  ,m2=2m2   ,d=d/2
According to Newton’s law of gravitation
F’=Gm1m2/d2
Or F’=G2m12m2/(d/2)2
Or F’=4(Gm1m2)/d2/4
Or F’=4×4(Gm1m2)/d2
From eqn (i)
 F’=16F
؞The force will be 16F the initial force.
  3.)Gravitational force or weight produced between two bodies is 5N when they are at the distance of 5m.How much gravitational force or weight is produced when they are at distance of 10m.
Given,
1st condition
Gravitational force (F1)=5N
Distance (d)=5m
From Newton’s law of gravitation
F1=Gm1m2/d2
Or 5=Gm1m2/52
؞Gm1m2=5×25     ㅡ   i)
2nd condition
distance (d)=10m
gravitational force (F2)=?
From Newton’s law of gravitation
F2=Gm1m2/d2
0r F2=5×25/102
Or F2=125/100
؞F2=1.25N
Gravitational force of 1.25N is produced when given object is kept at 10m distance.

4.)Gravitational force produced between two bodies is 5N what will be the new gravitational force if the distance  between them is (i)Halved (ii) doubled.
Given ,
1st condition
Gravitational force(F1)=5N
From Newton’s law of gravitation
F1=Gm1m2/d2
5=Gm1m2/d2          ―       i)
i)2nd condition
Distance(d)=d/2
Gravitational force (F2) =?
From  Newton’s law of gravitation
F2=Gm1m2/d2
0r F2=Gm1m2/(d/2)2
Or F2=Gm1m2/d2/4
Or F2=4(Gm1m2/d2)
From eqn (i)
F2 =4×5
؞F2=20N
Gravitational force of 20Nis produced when given object is kept at halved distance with initial distance.
(ii)2nd condition
Distance(d)=2d
Gravitational force (F2) =?
From Newton’s law of gravitation
F2=Gm1m2/d2
Or F2=Gm1m2/(2d)2
Or F2=Gm1m2/4d2
Or F2=1/4(Gm1m2/d2)
From eqn (i)
Or F2=1×5/4
؞ F2=5/4N
Gravitational force of 5/4N is produced when object is kept at doubled distance with initial distance.
5.)If a person can lift a load of 60kg on the surface of earth .How much load can lift on the surface of moon .(gE=9.8m/s2 and gM=1.66m/s2)
Given,
Mass lift on earth(m)=60kg
Acceleration due to gravity of earth(gE)=9.8m/s2
Acceleration due to gravity of moon(gM)=1.66m/s2
Mass lift on moon (m)=?
By formula
Weight lift on earth (WE)=Weight lift on moon(WM)
 MgE=MgM
Or 60×9.8=M×1.66
M=60×9.8/1.66
؞Mass lift on the surface of moon (m)=354.21N     
6.)A man is capable of jumping 1m on the surface of earth .How height does he jumps on the surface of moon.?(gE=9.8m/s2 and gM=1.66m/s2)
Given,
Jump on the earth (h)=1m
Jump on the moon (h) =?
By formula
Height jump on earth(h)×gE = height jump on moon(h)×gM
Or 1×9.8 =height jump on moon(h) ×1.66
Or height jump on moon(h)=1×9.8/1.66
؞Height jump on the surface of moon(h)=5.90 or 6m

7.)What is force of attraction between two object each of mass 1kg separated by 1m distance ?
Given,
Mass of 1st object (m1)=1kg
Mass of 2nd object(m2)=1kg
Distance(d)=1m
Gravitational force (F)=?
By formula
F=Gm1m2/d2
 Or F =6.67 ×10-11×1×1 /12
Or, F=6.67×10-11 N                                                                       
 ؞Gravitational force(F)=6.67×10-11N
8.)The mass of venus  and sun are 4.89×1024kg and 2×1030kg respectively and distance between them is 1.072×108km.Find out the gravitational force between them.
Given
Mass of venus(m1)=4.89×1020kg
Mass of sun (m2)=2×1030kg
Distance(d)=1.072×108km
                     =1.072×1011m
Gravitational force (F)=?
  by formula,
F=Gm1m2/d2
Or ,F=6.67×10-11×4.89×1024×1030   /(1.072×1011)2
 Or,F=65.23×1043  /   1.14×1022
Gravitational force(F)=5.72×1022N
9.) If the mass of mars is 6×1023kg and that of earth is 6×1024kg and the gravitational force between them is 6.67×1016N,calculate the distance between their centers ?
Given,
Mass of mars (m1)=6×1023kg
Mass of earth(m2)=6×1024kg
Gravitational force (F)=6.67×1016N
Distance (d)=?
 By formula
F=Gm1m2   /    d2
or 6.67 ×1016=     6.67×10-11×6×1023×6×1024 / d2
 d2 =        6.67×10-11×6×1023×6×1024   /    (6.67×1016)2
d2 =36×1020
d= 6×1010m
Distance (d)=6×1010m

10.) The Mount Everest is 8848 m above the sea level. What is acceleration due gravity at this height? If the value of acceleration due to gravity at the gravity at the earth surface  is 9.8m/s2 and radius of earth is 6.4×106.
Given,
Height of Mount Everest (h)=8848m
Acceleration due to gravity surface(g)=9.8m/s2
Acceleration due to gravity at height(g’)=?
Radius of earth (R)=6.4×106m
By formula
g’ =(R/R+h)2×g
g’ =(6.4×106/6.4×106+8848)2×9.8
or g’ =40.96 ×1012    ×9.8 /     41.07×1012
Or Acceleration due to gravity( g’ )=9.78 m/s2  
11.)The mass and radius of earth are 6×1024 and6.4×106m respectively. Calculate the acceleration due to gravity at the top of Mt. Everest of height 8848m from the sea level .Also find out the weight of a person whose mass is 80kg on the height.
Given,
Mass of earth(M)=6×1024kg
Radius of earth(R)=6.4×106m
Height (h)=8848m
Mass of man(m)=80kg
Acceleration due gravity(g)=?
 By formula
g =GM/(R+h)2
or g =    6.67×10-11×6×1024   /(6.4×106+8848)
 Or g=    40.02×1013   /   (6408848)2
Or g=  40.02×1013  /        4.10×1013
 g=9.76m/s2
Acceleration due to gravity at the top of Mt. Everest =9.76m/s2
Also,
Weight of man(w)=m×g
                                          =80×9.76
                                          =780.8N
12.)What should be height from the surface of earth so that we can get the acceleration due to gravity 6m/s2.The mass of the earth and radius are 6×1024kg and 6400km respectively.
Given,
Acceleration due to gravity at height(h)=6m/s2
Mass of earth(M)=6×1024kg
Radius of earth(R)=6400km=6400×1000m=6.4×106m
Height from the earth surface(h)=?
By formula
g = GM/(R+h)2
or 6 =6.67×-11×6×102  /     (R+h)2
or (R+h)2 =40.02×1013  /    6
Or (R+h)2  =66.7×1012
Or R+h = ×1012
Or R+h =8.16×106
Or h =8.16×106-R
Or h =8.16×106-6.4×106
؞ Height (h)=1.76×106m
Therefore at the height of 1.76×106m from the earth surface we get acceleration due to gravity of 6m/s2.

13.) The mass of Jupiter is 319 times greater than the mass of earth and the radius is 11times greater than the radius of earth .If the acceleration due to gravity on the earth surface is 9.8m/s2.Calculate acceleration due to gravity on the surface of Jupiter .
Given,
Mass of Jupiter (Mj)=319ME
Radius of Jupiter(Rj)=11RE
Acceleration due to gravity of earth(gE)=9.8m/s2
Acceleration due to gravity of Jupiter (gj)=?
According to Newton’s law of gravitation
gE =GME/RE2 for earth                                               (i)
gJ =GMJ/RJ2 For jupiter                                             (ii)
Dividing eqn (i) by eqn (ii)
 gE /  gJ  =GME ×RJ2  /     GMJ×RE2
gE  / gJ  =GME× (11 RE)2  /    G319ME×RE2
or gE/gJ =121/319
gJ = 319×9.8  /121        
؞ Acceleration due to gravity on the surface of Jupiter (gJ) =25.83 m/s2       
14.)A stone is dropped freely from 20m height of tower .If reach ground in 2 sec. .Calculate the acceleration due gravity of that  stone .
Given,
Initial velocity (u)= 0m/s
Height (h) = 20m
Time taken (t) =2 sec
Acceleration due to gravity(g) =?
By formula
Height(h) =ut +1/2 gt2
Or 20 =0×2+1/2×g×22
Or 20 =0+2g
Or g =20/2
؞Acceleration due to gravity (g)=10 m/s2
15.)A body thrown vertically from earth surface and took  16 sec. to return to its original position .find out the initial velocity (The resistance is considered as zero)
Given,
Final velocity (V)=0m/s
Acceleration due gravity (g) = -9.8 m/s2
Time taken to reach its height  (t)=16/2 =8 sec.
Initial velocity(u) = ?
By formula
V =u+gt
Or 0 =u+(-9.8)×8
؞u =78.4 m/s
Therefore initial velocity (u)=78.4m/s


Unit-     8         Pressure

Pressure:-The force acting normally on per unit area is called pressure .Its S.I. unit Pascal or N/m2.It is a scalar quantity.
              Pressure (P)= Force(F)/Area(A)
                               P   =  F/ A

Relation between pressure ,force and area:-
i)When force is applied more pressure will be more and when force is applied less pressure will be less. If area is kept constant.
P∞F                                     (i)
ii)When force is applied on greater area pressure will be less and when force is applied on less area pressure will be more. If force is kept constant.
p∞1/A                                 (ii)

I Pa Pressure: The pressure produced by applying 1N force on 1m2 area is called 1 pa pressure.
                        1 pa = 1N/1m2

Prove that P= F/A
P =Pressure, F = force  ,  A =Area
According to relation between pressure ,force and area.
P∞F                                         (i)
P∞1/A                                  (ii)
Combing eqn (i) and (ii)
P∞F/A
P = KF/A (where k is constant)
Or P= KF/A                                   (iii)
According to definition 1 Pa ,if F = 1N, A = 1m2 then P = 1pa
Now, we get
1 =k.1 /1
؞K =1
Again,
  Putting the value of k in eqn (iii)
 Or P = 1 F/A
؞P =F/A Proved 

Difference between force and pressure

Force

Pressure

1.)A physical quantity that change the state of an object.

ii) its S.I. unit N

iii) It is a vector quantity.

iv) Force(F) =mass ×acceleration(a) or acceleration due to gravity(g)

F =m× a or g

1.)The force acting normally on per unit area is called pressure .

ii) Its S.I. unit is pascal.

iii) It is a scalar quantity.

iv) Pressure (P)= Force(F)/Area(A)

P = F/A

1.)A man exerts more pressure when he stand with one foot than when he stand on two foots, why ?
Ans. The area of one foot is less than that of two foots so a man exert more pressure he stand with two foots than with one foot ,because we know that
P∞1/A .
2.)Basses and truck have broad and double wheeled tyeres, why?
Ans. The areas of broad or doubled tyeres is more so give more less pressure on road and easily can carry heavy load .Therefore busses and trucks have broad and doubled tieres, because we know that P∞1/A
3.The studs are made on the sole of football player’s  boot ,why?

Ans. The studs of sole on the football players boot reduce the area of sole and give more pressure on the ground ,which prevent the player from falling and sliding .Therefore studs are made on the sole of football player’s boot, because we know that P∞1/A.
4.)The backside wheel of tractor are made larger and flat ,why?
Ans. The larger and flat wheel have more area, so  give less  pressure on the road and can easily move during ploughing, threshing etc. Therefore backside wheel of tractor are made larger and flat, because we know that P∞1/A.
 
Liquid pressure:- The thrust exerted by a liquid per unit area is called liquid pressure .Its S.I. unit Pascal or N/m2.
Liquid Pressure (P) = d×g×h
Where d= density of liquid ,g = acceleration due to gravity , h = depth of liquid
Factor affecting liquid pressure:-
i)density of liquid(d)
ii)Acceleration due to gravity (g)
iii)depth of liquid (h)
General laws of liquids pressure:-
i)The pressure of liquid is directly proportional to the depth of liquid. P∞h
ii)At the same depth the pressure of the liquid is same in all direction .
iii)Pressure of liquid is directly proportional to density of liquid .  P∞d
iv)The pressure of liquid does depend upon the shape and size of container .
v) The liquid finds its own level .
Prove that   P=d×g×h
According to definition of pressure
P =F/A
Or P =m×g/  A         ( F=mg )
Or P = d×v×g/  A  (m=d×v)
Or P = d×g×A×h/  A  (V =A xh)
؞ P =d×g×h Proved  

1.)The speed of flow of water out of a tap of up floor is less than that of the down floor ,why ?
Ans. The depth of liquid column of down floor is more than that of up floor. Therefore speed of flow of water is more at tap of down floor than that of tap of up floor, because we know that P∞d .
2.)What change in the pressure at the bottom of a drum filled with water. If it is brought to Himalaya from terai ?write with reason .
Ans. The pressure at the bottom of drum decrease, if water filled drum is brought from terai region to Himalaya region because The value of g is less at Himalaya region than that Terai region, We know that P∞g .
3.)While the building a dam for water reservoir the base is made wide, why ?
Ans. The depth liquid column of base of dam of water reservoir is more than that of upper portion,so base liquid column give  more upthrust than that of upper portion. Therefore base of dam of water reservoir is made wide .because we know that  p∞h 
4.)As the given fig the tank with capacity 1000 liter has greater cross sectional area than that with capacity 500 liter. Answer the following questions. 

i)Whose bottom experience more pressure, if both contain equal volume of water ?
Ans. The 1000L tank of bottom experience less pressure than that of 500 L tank of bottom because due to more cross sectional area of 1000L tank the depth of liquid column less than that of 500L tank because we know that P∞h
ii) If depth of water are equal in both which one experience more pressure at the bottom?
Ans. If both contain same depth of water the pressure exerted on the bottom of tank will be same.
iii) On which factors does the pressure of liquid depend ?
Ans. The liquid pressure depend on following factors ie i) density of liquid(d) ii)Acceleration due to gravity(g) iii) depth of liquid(h)
 
Upthrust :- When a body is  immersed in a liquid exert an upward force on the body is called upthrust.     Or
An upward force is experienced by an object ,when it is partially or wholly immersed in a liquid is called upthrust or buoyant force . its S.I. unit is N.
              Upthrust (U)=d×g×h×A
Where, d= density of liquid ,g= acceleration due to gravity,   h= depth of liquid ,A = area of the object
 Upthrust of liquid = Wt. of body in air –wt of the  body in the liquid
Or Upthrust of liquid = loss of wt of object in the liquid

Cause of upthrust:

When a body is immersed in liquid in a liquid the lateral pressure experience by the body mutually cancel each other ,but downward pressure and downward force acting on the body is always than that of upward pressure and force acting on body .Therefore resultant force acting between upward and downward  force i.e. cause of upthrust force or resultant force is known as upthrust.
 
Prove that U= d×g×A×(h2-h1),  ( using Archemedes’ principle)    
Or U = d×g×h×A              
Or U=d×g×v                     
Or U=mg or w                          
Or  Upthrust =displace of wt. of liquid (w) 

Suppose

 A body PQRS of height =h
Cross sectional area =A
Densety of liquid =
Height of liquid column above surface PQ =h1
Height of liquid column above surface RS=h2
Now,
Pressure exerted on upper surface PQ(P1)=d×g×h1
Or Downward upthrust exerted on upward surface(F1)=P1×A
     Or F1 =d×g×h1×A
Again,Pressure exerted on lower surface RS(P2)=d×g×h2
Or Upward upthrust exerted on lower surface(F2)=P2×A
Or F2=d×g×h2×A

؞Resultant force or Upthrust (U)=F2-F1
Or U=d×g×h2×A - d×g×h1×A
Or U=d×g×A(h2-h1)
Or U=d×g×h×A          (because h2-h1 =h)
Or U=d×g×v                 ( because V=A×h)
Or U=m×g                   (because  m=d×V)
Or U = w          (because w=m×g)
؞Upthrust = Weight of displace of liquid 

1.)An egg float in salt water but sink in fresh water, why?

Ans. The density of salt water is more than that of density fresh water, so salt water give more upthrust than that of fresh water. Therefore an egg float on salt water but sink in fresh water, because we know that U∞d.

2.)It more easy to swim in sea water than that of river water why ?

Ans. The density of salty sea water is than of river water so sea water gives  more upthrust than that of river water. Therefore it is more easy to swim in sea water than that of river water ,because we know that U∞d.

3.)It is more easy to pull bucket inside water than air, why ?

Ans. The density of water is more than that of air so water give more upthrust than that of air. Therefore it is more easy to pull bucket inside water than that of air because we know that U∞d.

4.)It is difficult to sink an empty plastic bottle in water ,why?

Ans.The density of air filled empty bottle is very less than that of water so, water give more upthrust than that of empty plastic bottle .Therefore it is difficult to sink empty bottle in water because we know that U∞d. 

5.) What is the weight of an object floating on the surface of water? Explain.

 

Ans. The weight of an floating object is always zero, because at this condition the  force acting the downwards and the upward is equal and opposite .
 

Law of floatation:- An object that floats on liquid medium displace the liquid equal to its weight is known as law of floatation.
Or An floating object displace liquid equal to its weight is known as  floatation .

Wt. of displace of liquid = Wt. of the floating an object

Verification of law of floatatio
                      
 Suppose,a beaker having spout containing water is kept on a ureka can .Take a wooden block having wt.=w1, then ,it is kept in beaker and it displace water and collected in a beaker  having wt .= w2
Now, It is found that
Wt of wooden block = wt of displace of liquid
             W1 = W2
It show that or verify floating object displace liquid equal to its weight
Instruments based on law of floatation:-
i)Hydrometer ii) Lactometer

 1.)An iron nail sink in water but a ship made up iron float in water, why ?

Ans. The volume of iron ship is more than that of iron nail so, iron ship can displace liquid equal to its weight but iron nail can’t displace liquid equal to its weight .Therefore according to law of floatation iron nail sink in water but ship a ship made up iron float on water .
2.) How much water a girl weighting 450 N should displace in order to float in water .
Ans.A girl weighting 450 N should displace 450N water in order to float in water because according to law of floatation the wt. of floating body = wt. of displace of water.  
Pascal’s Law:- When pressure is applied on the liquid contained in a closed  container .It transmitted equally in all direction is known as pascal’s law .



Instruments based  on pascal’s law:-
i)Hydraulic press ii) Hydraulic jack iii) Hydraulic lift iv) Hydraulic break
i-Hydraulic press:- An U shaped simple machine based on pascal’s law, which convert small force into large force is called Hydraulic Press .It consist of two piston, area of one piston small and other piston is large . 

                  
Principle of hydraulic press:- It states that ,when small force is applied on small piston it change into large force on bigger piston .
 

Characteristics of liquid on the basis of which hydraulic press is constructed :-
i)Liquid transmits pressure equally in all direction.
ii)Liquid is incompressible .
 Uses of hydraulic Press:-
i)It used for pressing books ,cotton goods.
ii)It is used for extracting juice of fruits ,seeds etc.
iii)It is used to gives specific shape to metal and punching hole in metal
iv)It is used for pressing plywood ,cardboard etc.
Prove that Hydraulic Press is an effort multiplier, or
              F2/F1 =A2/A1
             
Suppose ,A U shaped  vessel contain a liquid is provided with 2 piston, cross sectional area of small piston =A1
Cross sectional area of large piston=A2
Then, force F1 is applied on small piston and pressure exerted on small piston P=F1/A1

According to pascal’s law pressure exerted on small piston is transmitted on large piston.
Therefore , Pressure exerted on large piston =F1/A1
Again,
Upward force exerted on large piston= F2=P2×A2
Or F2 =F1   ×A2 /   A1
؞   F2  / F1     =       A2 /   A1
                                              Proved
Or A2>A1  gives F2>F1
Therefore, small force F1 can change large force F2  on Large piston o act as force multiplier.

ii-Hydraulic jack:-

Construction and Working
The main components of a hydraulic a hydraulic jack  system are:
1.Base: A sturdy base that provides support for the jack.
2.Reservoir: A container that holds the hydraulic fluid.
3.Pump: A device that creates hydraulic pressure.
4.Ram: A piston that extends and retracts to raise or lower the load.
5.Cylinder: A tube that houses the ram.
6.Lift arm: A lever that connects the ram to the load.
7.Release valve: A valve that releases hydraulic pressure to lower the load.
Uses of hydraulic jack:-


1.)It is used for lifting automobile i.e. truck ,bus etc in service station.





Constructions and Working
The main components of a hydraulic car brake system are:
1.     Master or main cylinder(P) : This is the pump that generates the hydraulic pressure. When you press the brake pedal, it pushes a piston inside the master cylinder, which forces brake fluid out of the cylinder and into the brake lines.
2.     Brake lines: These are flexible T  tubes that carry brake fluid from the master cylinder to the wheel or slave  cylinders (Q).
3.     Wheel cylinders or Slave cylinder (Q): These are cylinders located near each wheel. When brake fluid enters the wheel cylinder, it pushes B1 and B2 piston inside the wheel  cylinder, which forces the brake pads against the brake rotors.

1.  5.   Brake pads: These are the friction material that rubs against the brake rotors to slow down the car.

1.   6.  Brake rotors: These are the discs that the brake pads rub against. They are made of a special material that can withstand the high temperatures generated during braking.

2.  7.   Calipers: These are the housing units that hold the brake pads in place





Uses of hydraulic break :-

i)it is used for stop heavy automobiles i.e. truck ,car, bus etc by applying small force.

Hydraulic lift :-

Construction and Working

The main components of a hydraulic lift system are:
1.Base: The base is the sturdy foundation of the hydraulic lift. It provides support for the entire structure and prevents it from tipping over.
2.Reservoir: The reservoir is a container that holds the hydraulic fluid. The hydraulic fluid is responsible for transferring power from the pump to the ram, which raises and lowers the load.
3.Pump: The pump is a device that creates hydraulic pressure. It converts mechanical energy from the pump handle or motor into hydraulic energy in the form of pressurized fluid.
4.Ram: The ram is a piston that extends and retracts to raise or lower the load. It is the heart of the hydraulic lift,
5.Cylinder: The cylinder is a tube that houses the ram. It provides a sealed enclosure for the ram to move freely and prevents the hydraulic fluid from leaking out.
6. Lift arm: The lift arm is a lever that connects the ram to the load. It amplifies the force of the ram to lift heavier loads.
7.Release valve: The release valve is a valve that releases hydraulic pressure to lower the load. It allows the pressurized fluid to flow back to the reservoir, causing the ram to retract and the load to descend.

Uses of hydraulic lift :-It used in hospital ,hotels etc to provide easy service.

Archimedes’ principle:-
It states that “When a body is body is partially or wholly immersed  in a liquid .It experience an upthrust (loss of weight ) is equal to displace of liquid by it” .
  According to Archimedes’ principle ,Wt. of object in air = Wt. object in liquid + Wt of object in liquid

Instruments based on Archimedes' Principle
i)Ship      ii)SubmarineAccording to Archimedes’ principle ,Wt. of object in air = Wt. object in liquid + Wt of object in liquid                                  

Experimental verification of Archimedes’ Principle:-


Suppose ,wt of in air =W1
 Wt. of object in water =W2
؞Upthrust =w1 – w2                                                     (i)
Wt. of beaker =W3
Wt . of beaker with displace of liquid =W4
؞ Wt of displace of liquid =W4 –W3                             (ii)
After calculation the value of (i) and (ii)
         W1 – W2      =   W4  - W3
Or  It show that or verify , Upthrust  = Wt. of displace of liquid or Archimedes’ principle.


Density :-Mass per unit volume is called density. Its S.I. unit is kg/m3  and C.G.S. unit is gm/cm3.
Density (d)= Mass(m)/Volume(v)
  D =         m /  V

Example:- density of water =1000kg/m3  or 1gm/cm3
i)Convert 1000kg /m3 into gm/cm3
    = 1000 ×1000  / 100×100×100
    = 1gm/cm3
ii)Convert 1gm/cm3 into kg/m3
= 1×100×100×100/  1000
  =1000kg/m3

Relation between density of a body and floatation:-

i)When the density of an object is greater than that of density liquid then sink in the object.
ii)When the density of an object is less than that of density of the liquid then object float on the liquid .
iii)When the density of an object is equal to  the density of the liquid then the object floats just inside the surface of the liquid.
Relative density :-(R.D.):-The ratio of the density of the substance to the density of the water at 4  is called relative density .It have no unit .
 Relative density (R.D.) =Density of  the substance /   Density of substance at 4
Hydrometer and Lactometer :- The instrument which is used to measure density  to liquid is called hydrometer .It is based on principle law of floatation.
 The instrument which is used to measure density of milk is called lactometer. It is also based on principle of law of floatation .
                                              
1.)The gravity of bulb of hydrometer is made heavier ,why ?
Ans. The heavier bulb of hydrometer help it to into float up right in stable  equilibrium .Therefore the bulb of hydrometer is made heavier .
 2.)The floatation bulb of hydrometer is made small ,why ?
Ans. The floatation bulb of hydrometer is made small due to this whole hydrometer does not float on the denser liquid because denser liquid provides more upthrust. 
3.)The stem of hydrometer is marked from top to bottom, why ?
Ans Hydrometer sink deeper in less density of liquid or the length  sink portion of hydrometer is inversely proportional to the density of the liquids .Therefore, the stem of hydrometer is marked from top to bottom.
Atmospheric pressure:-The pressure exerted by atmospheric air per unit area on surface of earth is called atmospheric pressure. The weight of air itself is the cause of atmospheric pressure. Its S.I. unit is N/m2 or mmHg(millimeter mercury) and measured by help of   Barometer.
Barometer .The atmospheric pressure at sea level i.e. 5N/m2 or 760mmHg, is also called standard atmospheric pressure.
 Atmospheric pressure(p) = d×g×h    Where d=density of air  g= Acceleration due to gravity ,h=depth of air
Air pressure :-The pressure exerted by gas per unit area  enclosed in vessel i.e. balloon, is called air pressure .

Uses of atmospherics pressure:-
1)It help for movement of air due to change in atmosphere .
2)We can fill ink inside pen ,medicine inside syringe ,air inside tube of bus ,car bike etc.
3)Water pump work by help of atmospheric pressure .

1.)When we go to higher altitude ,nose bleeding occurs ,why?
Ans. When we go to higher altitude depth of atmosphere decreases, so human blood pressure become more than that of atmospheric pressure due this blood vessel present inside nose ,ear feel more pressure and rupture .Therefore, when we go to higher altitude bleeding occurs .
2.)A air filled balloon at higher altitude brusts ,why ?
Ans. In air filled balloon at higher altitude ,the atmospheric pressure become less than that of air pressure inside balloon, so air filled balloon at higher altitude brusts ,because we know that atmospheric pressure decreases due increase of height  .

Numerical  problems
Formula:- 
1)P =  F/A
2)  P=d×g×h
3) U= d×g×h×A
4)F2/F1  =  A2/A1
5) d =M/V     
6) Wt. of displace of liquid = Wt of floating body
7) Volume of displace of liquid =Volume of immersed portion of an object

1)Density of iron is 7600kg/m3 .What will be the mass of iron block with dimension of 4cm ×15cm×20cm.
Given,
Volume iron block (v) l×b×h
                                    =4×15×20   =1200cm3 /100×100×100
                                    =0.0012m3
Density of iron (d)=7600kg/m3
Mass of iron block (m) =?
By formula
m=d×v
 =7600 ×0.0012
 ؞m= 9.12 kg
Mass of iron block (m) =9.12 kg
2.)A load of 2000N is be lifted by hydraulic press whose large piston cylinder has area of cross sectional 4m2. If a small cylinder has cross sectional of 40cm2 .Calculate the force necessary to apply on the piston of the small cylinder .
Given
,Load on large cylinder (F2)=2000N
Area of large cylinder (A2) =4m2
Area of small cylinder(A1)=40cm2 = 40/100×100  =0.004m2
Force apply on small cylinder (F1)=?
By formula
F2/F1      =A2/A1
Or  2000/F1 =4/0.004
Or F1= 2000×0.004  /4
F1 =2 N
Force applied on small piston (F1) =2N

3.)Observe the given fig and answer the following questions .
i)What is pressure exerted on the liquid by the load.
ii)What is pressure acted on X ?
iii)Calculate the area of small cylinder ?

 Given,
Force on small piston (F1)=200N
Force on large piston(F2)=12000N
Area of large piston(A2)=2.5m2
i)by formula
P =F2/A2
  = 12000/2.5
=4800 pa.
ii)According to pascal’s  pressure exerted on large piston equal to small piston .
؞pressure exerted on piston X=4800 Pa.
iii)by formula
Area of small piston (A1)=   A1 ×F1   /  F2
   =200×2.5/12000
A2  =0.041 m2
Therefore area of small piston (A1)=0.04m2

4.)Piston A,B;and C are the apparatus given in the diagram are supposed to be frictionless .What is the area of the piston B? What is force exerted on piston C?

Given,
Force at piston A (F)=250N
Area of piston A(A)=20cm2
Force at piston B(F)=375N
Area at piston C(A)=10cm2
By formula
Pressure of piston A(P) =F/A
Or P=375/10
 Pressure(P)=12.5 Pa
ii)by formula
Area of piston B(A) =F/P
Or A =
؞Area (A)=30 cm2
iii) by formula
Force exerted on piston C(F)=P×A

Or F = 12.5 ×10

؞Fore exerted on piston C (F) = 125 N.

5.) An iceberg of 50cm×30cm×20cm float on water .The density of ice berg  and water are 900kg/m3 and1000kg/m3 respectively .Calculate the mass of water displaced and also find out the portion of iceberg that remains above the water surface .
Given,
Volume of iceberg (v) l×b×h
 Or V= 50×30×20      =30000cm3
Or V =0.03 m3
Density of water (d)=10000kg/m3
Density of iceberg (d)= 900kg/m3
Now, i) By formula
Mass of iceberg (m) d×v
Or m= 900 ×0.03
 mass of iceberg (m) 27 kg
we know that .Mass of displaced of liuid  =mass of floating body
              or                                                = 27 kg
Therefore mass of displaced of water =27 kg
Again . volume of displaced of water(v)=m/d
 Or                                                       v=27/1000    =0.027m3
We know that , volume of immersed portion of an object = volume of displaced  of liquid
Therefore, volume of immersed portion of iceberg = 0.027 m3
By formula ,
Immersed portion of an object =Volume of immersed portion of an object /Total volume of an object
Or immersed portion of iceberg =   0.027/0.03     =9/10= 0.9 parts
Therefore above portion of iceberg = 1- 0.9 =0.1 part 

6.) A rectangular body is completely dipped in water as shown in fig .The upper or lower surface area  it is 2m2.find the upthrust acted upon it due to water .(density of water is 1000kg/m3).

Given,
Area of body (A)=2m2
Height of given body(h)=h2- h1
Or       h= 7-3 =4cm
Density of water (d)=1000kg/m3
Upthrust (U)= ?
By formula
U =d×g×h×A
Or U=1000×9.8×4×2
Therefore (U)= 7800N.

8.)Study the given diagram and answer the questions .
i)What is weight of an object in air?
ii)How much upthrust is exerted by the liquid on the object.
iii)Calculate the mass of object ?
iv)In which law this experiment based ?


Ans. i)By formula
Weight of object in air = wt. of object in liquid +wt of displaced of liquid
Or                         =10+2   =  12N
ii)Upthrust =wt of displaced of liquid
or                  =2N
 iii)By formula
Mass (m)  =w/g  
Or m=12/9.8  = 1.22Kg
iV) This experiment based on Archimedes’ principle.

9.)Different weight of a pieces of stone weighting in three different media air ,water and salt solution are given below.

Media

Weight

A

30N

B

20N

C

25N

i)Which of them are air, water and salt solution .
Ans. Maximum weight is in air due to minimum upthrust and minimum weight in salt due to maximum upthrust .
So, A=Air      B=Salt solution     C= water solution
ii)Find out the mass of water displaced by stone ?
AnsWeight of water displaced by the stone =30N-25N  =5N
Now, Mass o f displaced of water (m)    =5/9.8  =0.5 kg
iii)if 1  kg of stone is equal to 10N ,calculate the mass of stone in air .
Ans. Given,mass of 10 N stone = 1kg
So ,      “             “       1N = 1/10kg
Therefore ,mass of 30N =1/10×30 =3kg
10.)Densities of some substances are given in the table ,answer the following questions on the basis of table.

Substances

Density (gm/cm3)

A

11

B

8

C

0.9

i)If Mass of all are taken equal which one will have the largest volume?
Ans. Volume of substance is inversely proportional to the density of substance So if mass are equal’ Z’ substance  will have largest volume due least density.
ii)If all have equal volume ,which one will have largest mass ?
Ans.Mass all substances is directly proportional to the density of substances. So ‘A’ substance will have largest mass ,due to largest density .
iii) Among the above substance ,which one will float in water ?
Ans. Among A, B and C substances ,C will float in water because c has less density than that of water .

     Unit -9                   Heat

Thermal energy : The total kinetic energy of the atoms and molecules in an object is called thermal energy . Its S.I. unit  is  joule  and C.G.S. unit is calorie and measured by calorimeter Thermal energy  is directly  proportional to the faster moving the atoms and molecules of an object.
Examples of  thermal energy
i.) pot of boiling water: The water molecules are moving very quickly, which gives the water a high thermal energy.
ii.)A hot stove: The stove's metal atoms are vibrating rapidly, which also gives the stove a high thermal energy.

Heat :- The transfer of thermal energy from a hotter object to a colder object is called heat .it is a form of energy that gives the sensation of warmth. It represents the total kinetic energy of the molecules of an object.  Its S.I. unit  is  joule  and C.G.S. unit is calorie and measured by calorimeter .It is transmitted from one place to another place. The quantity heat of present  in an object is directly proportional to their mass or number of molecules and their kinetic energy .

 Examples of heat

i.)A cup of hot coffee: The coffee is hotter than your hand, so heat is transferred from the coffee to your hand. This makes your hand feel warm.
ii.)A metal spoon in a pot of hot soup: The spoon is colder than the soup, so heat is transferred from the soup to the spoon. This makes the spoon feel warm.
iii.)A person sitting in front of a fireplace: The person is warmed by the heat that is radiated from the fire.
iv.)A plant growing in the sun: The plant's leaves absorb the sun's heat, which helps the plant to grow.
          
One calorie or one calorie heat :- The amount of heat required to rise the temperature of 1gm of pure water by 1  is called 1caloie heat .
                         1cal =4.2 joule
We know that,
1kg( 1000gm) of water requires to raise the temp by 1                  = 4200 Joule heat    
 1gm of water requires to raise  the temp by 1  =        4200/1000     = 4.2 joule
Therefore ,1calorie  heat = 4.2 joule.
Effects of heat :-following are the effect of heat .            
i)It change the state of matter .
ii)It change the temperature of an object .
iii)It change the solubility of the substance .
iv)It is the cause of chemical change in an object 
 
v)It change the size or volume  of an object or Effect of heat on volume of object :The volume of a substance increases on heating and decreases on cooling, because when a substance is heated, its molecules absorb heat and vibrate and when absorb more heat energy ,they vibrate with more energy and expand. Therefore when solid is heated they change into liquid state and when liquid are heated they change into gases state. So a substance in a gases state expand the most and in the solid state expands the least on heating .For example when we heat milk, its volume increases which may overflow from the container.

1. )Fig shows the kinetic energy of different  molecules. calculate the average kinetic energy .

Average kinetic energy of                                                                     Molecules =   4+5+3+4/4
                =   4 joule  

Temperature  :-

The measure of  average kinetic energy of the atoms and molecules in an object is called Temperature. It is also called physical property of matter that describes the degree of hotness or coldness of an object. Its S.I. unit is is Kelvin (K) and measured by thermometer .It is not transmitted from one place to another place .The temperature of an object is directly proportional to the average kinetic energy molecules .
Anomalous Expansion of Water :Generally substances expand on heating and contract on cooling but when water at 00C is heated its volume decreases gradually till to 40C and then volume increase when heated above 40C . This unusual behavior shown by water from 00C to 40C is called anomalous expansion of water .The anomalous expansion property of water is useful for aquatic animals in cold countries .

At 00C water has maximum volume and minimum density .
But at 40C water has maximum density and minimum volume.
 
Advantages of anomalous expansion of water.
1. In cold countries, fishes and other aquatic animals can survive in the pond,the surface has frozen to ice.

Because the surface water gradually cools to 00C and freezes but the water of temperature 00C to 40C remains in the pond from top to bottom below the layer of ice. The layer of ice help to trap the heat as bad conducter of heat.
 2. Soft drinks bottles can be stores below the layer of frozen ice in the cold places to prevent them from freezing.
Disadvantages of anomalous expansion of water
1.cold countries water pipe burst in winter season
Because during winter season the  water  inside the pipe change into ice  and volume of ice is more than that of water so volume of water increases inside the pipe.
2. Fruits and vegetables get damaged during severe frost (कडा चिसो).
 Because during winter seasons the water inside the cell change into ice and the volume of ice is more than that of water so cells of fruits burst and damage.
i. Lips burst during winter season.
Because during winter seasons the water inside the cell change into ice and the volume of ice is more than that of water so cells of lips burst.

Specific heat capacity (SHC):- The amount heat required to the temperature of 1kg of masses by 10C  is  called specific heat capacity .Its S.I. unit is j/kg0 C
For example : specific heat capacity of water is 4200j/kg  and ice is 2100j/kg0 C
1.)Study the given table answer the question .

Substance(metal)

Specific heat capacity

A

900j/kg℃

B

700j/kg℃

C

500j/kg℃
i)What do you mean by statement that specific heat capacity of B is 700j/kg℃?
Ans.  It means that 700j heat is required to raise the temperature of 1kg of B metal by 1℃ .
ii)If equal amount of heat is given to equal mass of substance .Which one of given  substances will gain more temperature and which one of substance will gain low temperature ?
Ans.The substance C will gain more temperature and substance A will gain low temperature  because C metal have lowest and A have highest   specific heat capacity .
iii)If equal mass of substance at 2  temperature are kept on wax slab .Which  one will have make the  deepest  hole in wax slab ,why?
Ans. A metal will make the deepest hole in the wax slab ,because the specific heat capacity of A metal is the highest .
2.)Why water is used to cool the engine of vehicle ?
Ans. Water has highest specific heat capacity so it help to keep engine cool for long time .Therefore water is used to cool engine of vehicle .
3.)Water is used in hot water bag not other liquid  ,why?
Ans. Water has highest  specific heat capacity so, it help to keep warm body for long time .Therefore ,water is used in hot water bag .,
4.)In desert ,it is very hot during day and it is very cold during night ,why?
Ans. The surface of desert consist of sand which has very low specific heat capacity so, sand gain heat very quickly during day and loss heat very quickly during night .Therefore ,it is very hot during day and very cold during night .

Heat equation :- The amount heat gained or loss by an object (Q) is equal  to the product of the mass (m) ,specific heat capacity (s),and change in temperature (dt)  of an object is called heat equation .In short the heat equation is given :
Q = m×s×dt  or t                                         (i)
Where Q =Amount of heat lost or gained  ,m  = mass of an object ,  s = specific heat capacity , dt =change in temperature , t= Temperature
Prove that  Q = m×s×dt
Suppose, A body of mass m is heated to increase its temperature from  t1   To t2    by heat Q.
According to heat law
Heat loss or gained by a body is directly  proportional to the mass of a body and change in a temperature .
Q∝   m              一                           (i)
Q  ∝dt   or (dt=t2   -   t2  )    一            (ii)
Combining  eqn  (i) and  eqn (ii)
Q   ∝     m ×dt
Or  Q   = s×m×dt   (Where s is specific heat capacity ) 
   Q = m×s×dt     Proved  .
1 Joule heat  :- The amount of heat  required to raise the temperature by 1℃ of an object having mass 1 kg and specific heat capacity 1j/kg℃   is called 1 joule heat .
1 joule heat =1kg ×1j/kg℃ × 1℃

Calorimetry  :-The measurement of heat lost or gained by an object is called calorimetry .
Principle of calorimetry :-It states that, When a hot body is mixed with cold body ,the heat lost by hot  body is equal to heat gained by cold body .  ie
Heat lost by hot body  = Heat gained by cold body
Principle of thermal equilibrium :- It state that Heat always flow from higher temperature to lower temperature until the temperature of heat donor and heat receiver become equal .in short equation is given :
                m1s1(t1- t)  =m2s2(t – t2)         一                 (i)
Where,m1 =   mass of 1st  body    ,s1  = Specific heat capacity of 1st body ,
t1 = temperature of 1st  body
m2 = mass of 2nd body , s2 =s Specific heat capacity of 2nd body ,
t2 =temperature of 2nd body, t = final temperature .
1.)During high fever , wet clothes is kept on the forehead of the patient ,why ?
Ans. A wet clothe is kept  on the forehead of patient having high fever to absorb more heat from the head and water evaporates .It help to reduce high temperature of patient because we know that heat always flow from high temperature to low temperature .
2.)Some time ,tight bottle metal cap is dipped into hot water to open it ,why?.
Ans. When tight bottle metal  cap is dipped into hot water ,there will be unequal expansion ie. Cap expand before than that of glass so metal cap become lose and open easily .
3.)Water in the earthen pot remains cold in summer ,why ?
Ans. The earthen pot has so many pores on it .When water is heated inside and hot water oozes out (leakage slowly) through the pores into the atmosphere so cold water only remains inside the pot .Therefore ,water cool inside the earthen pot .
4.)Why do we sweat in summer ?
Ans. In summer, the atmospheric temperature goes up higher than that  of our normal body temperature ie .37℃ , so to maintain our body temperature ie 37℃ our body losses excesses heat by sweating .

Thermometer :- The instruments which is used to measure temperature is called thermometer .
Different types of thermometer and their working Principle
1. Liquid thermometer : A device used to measure temperature by using the expansion or contraction of a liquid like mercury, alcohol  is called liquid thermometer .
Structure of thermometer :-

It consist of long glass tube having a fine capillary tube. The lower end of glass tube consist of a bulb contains mercury or alcohol as thermometric liquid .Its outer body consist of a scale is called thermo-metric scale .
Principle of thermometer :- The  volume of liquid expands on heating and contract on cooling is known  as principle of thermometer 
Types of liquid thermometers:
1.Mercury thermometer: The freezing point of mercury is -39 ℃   and its boiling point is 357℃ ,so mercury thermometer is used to measure temperature at very hot place ie. Desert.
2.Alcohol thermometer: The freezing point of alcohol  is -117℃    and its boiling point is 78℃ ,so alcohol  thermometer is used to measure temperature at very cold place ie. Himalya

Thermometric liquid :-The liquids  which is filled in the bulb of thermometer to measure temperature are called thermo metrics liquid .They are :
1)Mercury :- Causes used as thermo metric liquid :-
i)Mercury is good conductor of heat .
ii)It is shiny and opaque .
iii)It is does not stick to the inner wall of capillary tube .
vi)The freezing point of mercury is -39 ℃   and its boiling point is 357℃ ,so mercury thermometer is used to measure temperature at very hot place ie. Desert.
2)Alcohol:- Causes used as thermo metric liquid :-
i)It Is good conductor of heat .
ii) It is does not stick to the inner wall of capillary tube .
iii) It is cheaper than that of mercury .
iv)Its expansion rate is six times more than that of mercury .
v) The freezing point of alcohol  is -117℃    and its boiling point is 78℃ ,so alcohol  thermometer is used to measure temperature at very cold place ie. Himalya
1.)The boiling temperature of water can not be measured with the help alcohol thermometer, why?
Ans. we know that ,boiling point alcohol thermometer is 78℃ but water is 100℃ so ,above 78℃ alcohol vaporize and can not give reading thermometer .Therefore ,boiling temperature of water can not be measured by alcohol thermometer .
2.)food is cooked faster in a pressure cooker than that in an open pot ,why?
Ans. When pressure inside the cooker increase then boiling point of water also increases ,so water boil above 100 ℃  and food is higher temperature therefore ,food cooked fast than that in an open pot , because we know that boiling point is directly proportional  to the pressure .

2.Digital thermometer : A device that measures temperature by using a sensor that detects changes in electrical resistance or voltage is called digital thermometer .The sensor is typically located in the tip of the thermometer and is made of a material that changes its resistance or voltage in response to changes in temperature.

Working principle of digital thermometer:
The sensor is connected to a circuit that measures the resistance or voltage of the sensor. The circuit then converts the resistance or voltage into a temperature reading, which is displayed on a digital screen.
Advantages of digital thermometers:
1.Accuracy: Digital thermometers are more accurate than most liquid thermometers.
2.Ease of use: Digital thermometers are easy to use and read.
3.Safety: Digital thermometers are safe to use, as they do not contain any mercury or other hazardous materials.
4.Versatility: Digital thermometers can be used to measure a wide range of temperatures, from very low temperatures to very high temperatures.

3.Radiation thermometer: A device that measures the temperature of an object by detecting the amount of  electromagnetic radiation emits by the object  is called radiation thermometer. It is also known as a pyrometer  . All objects emit electromagnetic radiation, and the amount of radiation emitted is related to the object's temperature. For example :an hotter object emits more radiation.

Working principle of radiation thermometer:
1.     The radiation emitted by the object is focused onto a detector
2.     The detector converts the radiation into an electrical signal.
3.     The electrical signal is amplified and processed to produce a temperature reading.
Advantages of radiation thermometers:
1.Non-contact measurement: Radiation thermometers can measure the temperature of an object without touching it, 
2.Fast response time: Radiation thermometers can measure temperature very quickly, 
3.High accuracy: Radiation thermometers can measure temperature with a high degree of accuracy.
Disadvantages of radiation thermometers:
1.Cost: It is expensive.
2.Limited range: Radiation thermometers typically have a limited range of temperatures that they can measure.
 
Calibration of Thermometer:
is The process of
 is The process of determining the scale in a thermometer is called Calibration of thermometer For this process, two fixed points, i.e.. lower fixed point and upper fixed point  is  determined.
A)Lower fixed point:
The temperature of pure melting ice at the standard temperature and pressure is called the lower fixed point. It is 0°C or 320F or 273 K at standard atmospheric pressure, i.e. 760 mmHg.

Activity:

To determine the lower fixed point of the thermometer, i.e. ice point 

i)At first take a glass funnel and keep some ice pieces into it.
ii)Take a thermometer and insert its bulb into ice pieces as shown in fig.
iii)As result, the level of mercury drops down in the capillary tube and shows a constant reading after sometime
Iv)The constant temperature is the melting point of ice. It is called the lower fixed point or ice point. Its value is 0°C or 32°F or 273 K.
B)Upper fixed point
The temperature of pure boiling water at the standard temperature and pressure is called the upper fixed point. It is 100°C or 2120C or 373 K at standard atmospheric pressure, i.e. 760 mm Hg.
Activity :
To determine the upper fixed point of the thermometer, i.e. steam point

i)Take a round bottom flask and keep some pure water into it .
ii)Insert a thermometer and a glass tube with the help of cork as shown in fig
iii)Take a Bunsen burner and boil the water in the flask for a while.
iv)Observes level of mercury in the thermometer.
v)When water is heated, the level of mercury rises up in the capillary tube. vi)When water boils, the thermometer shows a constant reading.
vii)The constant temperature is the boiling point of water. It is known as upper fixed point or steam point. Its value is 100°C or 212°F or 373 K

During calibration of a thermometer, first of all, the upper fixed point and the lower fixed point are determined. Then the distance between these two points is divided into 100 equal divisions in Celsius and Kelvin scale and into 180 equal divisions in Fahrenheit scale.
 
Temperature scale :-There are 3 major types of temperature scale :
i)Celsius Scale or Degree centigrade scale(0℃ ):-The scale in which lower fixed point is 0℃ and upper fixed point is 100℃ is called Celsius scale .In this scale the range between two points is divided into 100 equal  parts  and  in Celsius scale water freeze into ice at  0℃ and boil at 100℃.

ii)Degree Fahrenheit cale (℉  ) :-The scale in which lower fixed point is 32℉ and upper fixed point is 212℉    is called degree Fahrenheit scale .In this scale between two points is divided into 180 equal parts and in Fahrenheit scale, water  freeze into ice at 32  and boil at 212  .
3)Kelvin scale :-The scale in which lower fixed point is 273K and upper fixed is 373K is called Kelvin scale . In this scale the range between two points is divided into 100 equal parts and in Kelvin scale water freeze into ice at  273K and boil at 373 K.
The relation between different temperature scales :-
=C-0/100    =F-32/180    =K-273/100

 Numerical problems:-
i)            Q   = m×s×dt or t
ii)        m1s1 (t1 – t)  = m2s2(t –t2)
Note :-  -Specific heat capacity of water =4200j/kg℃
- Normal  temperature of water ,highest density of water ,lowest
   volume of water =4.℃
-highest volume ,lowest density of water =0℃
1.)2.1×105j of heat energy is required for 2kg of water to raise its temperature from 25℃ to 50℃. Find the specific heat capacity of water .
Given,
Amount of heat (Q)=2.1×105 j =210000j
Maas (m)= 5kg
Change in temperature(dt)=50℃ -25℃   =25℃
Specific heat capacity (s) =?
By formula
Q = m×s×dt
Or 21000 = 5×s×25
Or s=   210000/5x25=    4200 
Therefore ,Specific heat capacity (S) =4200 j/kg℃.

 2.)The temperature of 2kg of water is 10℃. and  8400j of heat is supplied in it ,what will be its final temperature or after it ?
Ans.Given,
Mass of water (m)= 2kg
Amount of heat (Q) = 8400j
Initial temperature (t1) =10℃.
Raise in temperature (t)=?
Final temperature (t2)= ?
By formula
Q =m×s×t
Or 8400  =2×4200×t
Or t =    84000/4200x2 =10℃.
Therefore ,raise of temperature (t) =10℃.
Again ,Final temperature (t2)=t1 + t
  Final temperature (t2) = 10 +10
                                                = 20℃.
3.)A beaker contains 0.2kg of water at 20  ,what will be its final temperature .if 0.3kg of water at 60  is added to it ?
Given ,
Mass 1st body (m1) =0.2kg
Specific heat capacity of 1st body (s1) =4200j/kg
Temperature of 1st body (t1) =20℃.
Again ,Mass of 2nd body (m2)=0.3kg
Specific heat capacity of 2nd body(s2)=4200j/kg  
Temperature of 2nd body (t2) =60℃.
Final temperature (t) =?
By formula
m1s1(t1 –t ) =m2s2(t –t2)
or 0.2 ×4200(20-t ) =0.3×4200(t- 60)
or 840(20-t) =1260 (t-60)
or 16800-840t =1260t-75600
or 2100t =92400
or t =   92400/2100  =44℃.
Therefore final temperature (t)=44℃.

 

  Unit -10                  Wave                       

Wave:-A periodic disturbance that carries energy away from an object through a medium during motion is called wave.

Electromagnetic wave :-The wave which are not affected by electric and magnetic field and do not need material medium for propagation are called electromagnetic wave .

For example :i)Gamma ray ii)X ray    iii)Ultra violet radiation iv) Visible light  v)Infra red radiation  vii)Micro wave  viii)Radio wave .

Common properties of electromagnetic wave :
1.Electromagnetic waves are non-mechanical waves. They do not require any material medium for propagation.
2. Electromagnetic waves travel with a constant velocity in vacuum. The speed of the waves is 3 x 108 m/s.
3. Electromagnetic waves are transverse in nature.
4.They are not deflected by electric or magnetic field.
5. They propagate by varying electric fields and magnetic fields, such that these two fields are at right angles to each other and at a right angle with the direction of propagation of the wave.
6. The ratio of the amplitudes of the electric field and the magnetic field is equal to the velocity of the wave.
7.They exhibit the properties of reflection and refraction .when electromagnetic wave passes from one medium to other medium ,its direction of travel ,speed and wave length changes but frequency remains unchanged .

Light:

Light is a form of electromagnetic wave that help the human eye to see or makes objects visible. Light is a type of energy It is made up of from tiny packets of energy called photons. Photons can travel through a vacuum.  They don't need a medium to travel .Light travels in a straight line at a speed of 300,000 kilo meters  per second .Light has many different properties, such as reflection, refraction, and diffraction.

Refraction of light :-
The bending of light from its original path when passing from one medium to another medium is called refraction of light .


Causes of refraction
The change in  the velocity of light on going from one medium from another medium  is causes of refraction of light .for example :The velocity of light in air is 3×105m/s but when it passes into water  it change into 2.2×108 m/s  and in glass it change into 2× 108 m/s.
Denser and rarer medium :The medium in which the velocity of light is less or having more density   in comparison to given other medium  is called denser medium .For example : In comparison to air and glass ,glass is denser medium to that of air
The medium in the velocity of light is more or having less density in comparison to given medium is called rarer medium .For example air is rarer medium to that of glass .

Incident ray :The path of the ray of light in the first medium is called incident ray .
Point of incidence :-The point where an incident ray strike on another or second medium is called the of incidence .
Normal:-A line drawn perpendicular to the boundary surface between two media is called a normal .
Angle of incidence :-The angle which makes the incidence ray with the normal is called angle of incidence .It is denoted by i
Refracted ray :-A ray of light which bends or deviates from its original path when passing second medium is called refracted ray .
Angle of refraction :-The angle which the refracted ray makes with the normal is called angle of refraction .It is denoted by r
Emergent Ray: The ray of light which emerges out of the second medium is called emergent ray .
Emergent Angle :The angle made by emergent ray to the normal is called emergent angle. It is denoted by e
Lateral Shift or Lateral displacement: The perpendicular distance between emergent ray and incident ray is called lateral shift or Lateral displacement .


Refraction in Glass slab:


                                                                        Fig . A


                                                                Fig.  B

                                                            Fig.  C

Laws of reflection of light :
1.)When the ray of light travel from rarer medium to denser medium ,it bends towards normal   or  i>r
2.)When the ray of light travel from denser medium to rarer medium, it bends away from the normal   or i<r
3.)The incident ray ,refracted ray and the normal line in the same plane and same point .
4.)The ratio of the sine angle of incidence(sine i) to  the sine angle of refraction(sine r) is a constant for a given pair of media  and this constant is called refractive index of the medium .It is also called Snell’s law .
 
Refractive index :- The ratio of the sine angle of incidence(sine i) to  the sine angle of refraction(sine r) is a constant for a given pair of media  and this constant is called refractive index of the medium. It is denoted by Mew ( μ ). For example : Refractive index of
Water =1.33,
Air = 1
Ice is= 1.31
Glass =1.5
Diamond =2.42
Alcohol=1.36
Kerosene=1.44
Glycerine =1.47
 
Refractive index( μ  ) =  Sine i /Sine r
                           Or
 Refractive index   (μ )    =Speed of light in air or vaccum or air(c)/Speed of light at that medium(v)
                             Or
 Refractive index (μ  ) =1/sine ic
                           Or
Refractive index (μ)   =Real depth /Apparent depth    
Factors affecting refractive index:
i)The nature of the medium
 ii)The wave length or colour of light
iii)Physical condition i.e. density, temperature etc.


Consequences of  refraction of light :
i)A star appear twinkling in the sky .
ii)A pond  appear shallow than its actual depth .
iii)An object placed in a denser medium when viewed from a rarer medium , appear to be at lesser depth .
iv)An object placed in a rarer medium hen viewed from a denser medium appear to be greater distance that of real distance .
v)A coin kept in vessel and not visible when seen from just below the edge of the vessel but can be seen from the same position when water is poured into the vessel .            

1.)Why does a pond appear shallow than its actual depth ?

Ans. The ray of light coming from the bottom of pond get refracted and bend away from the normal ,when refracted rays comes in our eyes give the apparent position of the bottom of pond , therefore the pond appear shallow than its actual  depth .

2.)A stick partially dipped in water seems to be bent ,Why ?

The ray of light coming from the  dipped portion of stick  get refracted and bends away from the normal , when refracted rays comes in our eyes give the apparent position of dipped portion of stick ,therefore stick partially dipped in water seems to be bent .

3.)A man standing in a pond sees a fish in the pond and tries to thrust a spear into it. he will succeed or not .Explain with reason .

Ans.

                                                    Fig. A

                                                             Fig.  B

He will not succeed , because the ray of light coming from the fish get refracted and bend away from the normal ,when refracted rays comes in our eyes give apparent  position of the fish .

4.The stars to appear to twinkle and change position why ?

Ans. The Earth's atmosphere is not uniform. It is made up of different layers of air of different densities and compositions. As result the light coming from  star  continuous get refracted (bent) and scattered .Therefore the stars to appear to twinkle and change position.

Critical angle and  Total internal reflection :

                                                            Fig.C

Critical angel :-
The angle incidence in denser medium for which the angle of refraction in the rarer medium is 900  is called critical angle .It is denoted by ic  ..  
The value of critical angel is 
 The value of critical angel is inversely proportional to the density medium.
Critical angle (ic ) = 1/density of medium(d)

 For Example :The value of critical angle of
Water =490
Alcohol=480
Kerosene=440
Glass =420
Diamond =240
Glycerine =430
The condition of critical angle :
i)The ray of light must passes from denser medium to rarer medium .
ii) Angle of refraction in 
 ii) Angle of refraction in 
 ii) Angle of refraction in rarer medium should be 900 .
 
Total internal reflectio of light:

                                                        Fig .B

When the ray of light travel from denser medium to rarer medium it bends away from the normal .If angle of incidence is greater than the critical angle then there is no reflection of light into the rarer medium and the rays are reflected  back into the denser medium or same medium .This phenomenon of reflection of light is known as total internal reflection of light .

Condition of total internal reflection of light :
i)The ray of light must passes from denser medium to rarer medium .
ii)Angle of incidence should be greater than critical angle .
Consequences of total reflection of light :-
i)Diamond sparkle with great brilliancy .
ii)During very hot weather mirage is observed on the hot desert of on the hot coal far road .
iii) Air bubbles shine inside water .

1.)Why does diamond sparkle with great brilliancy ?
Ans. The critical angle for diamond is 240 .When the ray of light inter into diamond they are incident always greater than that of critical .As result the ray of light undergoes total internal reflection multiple times due to this light comes out of diamond only at few points causing the emergent rays to be very bright ,Therefore diamond sparkle with great brilliancy .

                                                          Fig. A                                   

                                                                Fig.B

2.)Air bubbles shine inside water ,why?
Ans. The critical angle of water is 490 .When the ray of light inter into air bubble, the angle of incident always become greater than that of critical angle .As result the of light undergoes total internal reflection ,due to this air bubble shine inside the water .

3.Mirage :-

The apparent image of water which is seen in pitched road or desert during hot sunny days is called mirage .It is an optical illusion which can be observed generally in hot desert coal tarred road ,when inverted image of distant object is seen along with object in the pitch road or desert during hot sunny days .It is  caused due total internal reflection of light in upward direction .

Light pipe  and optical fiber:-

The  bending pipe  made up a bundle of optical or glass fibers through which light can pass in a curved line due to total reflection of light is called light pipe .It is used in endoscope. Doctors use the endoscope to examine internal part of our body i.e. food pipe ,stomach  etc.
Optical fiber :-A cylindrical wave made of transparent glass or plastic which pass light waves along its length by total internal reflection is  called optical fiber .It consist of 3 layers :
i)Core :-A place in the centre of fiber through which light travel is called core . 
ii)Cladding :- The outer optical materials that reflect the light back into the core is called cladding . 
iii)Coating :-The plastic buffer coating that protect the fiber is called coating .

Uses of optical fiber :-
i)It is used in long distance communication .
 ii)It is used in military application i.e. aircraft ,ships, tanks etc.
 iii)It is used in medical imaging i.e. endoscopes ,laproscopes etc.
Endoscopy: 


A medical procedure that allows the visualization of an internal parts of body through a device inserted directly into the organ is known as Endoscopy. It is used to examine the interior cavity of body i.e. food pipe, intestine, stomach etc for detecting bleeding, inflammation tumours etc. It act on the principle of total internal reflection.


                                        Fig.A
                                                                Fig.B

Keyhole surgery: A medical operation that is performed inside our bodies i.e. abdomen by utilizing small incisions and a small camera is called Keyhole surgery or Laparoscopy or minimally invasive surgery .In this process to treat the inside component a small hole is bored .A light pipe is used to visualize the internal part of the body. 

Dispersion of light (White light ):-

The process splitting of whit light into seven colours of light on passing through a glass prism is called dispersion of light .These seven colours of light are i)Red ii)Orange iii)Yellow iv) Green  v) Blue vi) Indigo vii) and violet .The seven colours of light are also denoted by “ROYG BIV”.
In seven colours of light red colour have largest wave length highest velocity and lowest angle of deviation and violet colour have smallest wave length lowest velocity and largest angle of deviation .

Causes of dispersion of light :-The dispersion of light occurs due to the different in angle of deviation of different colours of light when passing through a glass  prism , because when the white light ray enters a denser medium the velocity of light decreases and the different colours of light bend by different angles.
1.)Refraction from a prism disperse light but refraction from a glass slab does not .Explain  with reason .
Ans. A prism is triangular in shape , so when seven colours consisting  white light are incident on first surface they are bent towards the base .Then when they passes from glass to air or from second surface refract further from base .This increase the angle between rays and separate from each other .Therefore prism disperse white light into different colours of light .
 But ,the glass slab is rectangular in shape or consist of two prism joined at the diagonally so the rays of light get dispersed in first prism and combine in second prism to form white light , so glass slab can not disperses white light.

2.)Rainbow is seen when it is raining and sun rays pass through it .Why ?
Ans. When the raining stops ,a large number of tiny droplets of water are in the atmosphere .The water droplets act as small prism .So when white light rays from the sun into the atmosphere ,they are dispersed by the tiny droplets of water into seven colours .The seven colours of light appears in the form of a band and a rainbow is formed in the sky .

3.)Sun seems to be red during sun set and sunrise ,why ?
Ans. During sun set and sunrise ,sun rays travel greater distance through the atmosphere .The blue colour ,due to its high scattering capacity get scattered away and cannot reach to eyes but red colour having very low scattering capacity and reach our eyes .Therefore the sun appears red during sun set and rise .

4.)What characteristics property of light is responsible for the blue colour of the sky ?
Ans. The light from sun has to travel a long distance of earth in atmosphere before reaching the earth .The light get scattered in different direction by air molecules present in its path. But  the blue colour due to its high scattering capacity get scattered the most .Therefore the sky appears in blue colours .

Lens :- 
A transparent refracting medium bounded by two spherical a spherical surface is called lens.

Types of lens :- They are two types :-
1)Convex lens:-  i)The lens which is thicker in middle and thinner in edge is called convex lens .
ii)It converge parallel beam  of light after refraction so it is also called converging lens. It help burn paper due to its converging properties.
Iii) The power of convex lens +Dioptre (D) because it has positive focal length due to its real focus .
iv)It form the real and inverted image when the object is placed further from the lens and virtual image when object is placed between focus and optical center .

2.)Concave lens :- i)The which is thinner middle and thicker in edge is called concave lens .
ii)It diverge the parallel beam of light after refraction so it also called diverging lens .
iii)The power of concave lens is – Dioptre (D) because it has negative focal length due to its virtual image .
iv)It form always virtual and erect image .

Image:_When light ray coming from object falls on lens and get  refracted  ,then refracting rays produce a picture is called image is
Called image .They are two types :
i)Real image:-      The image which can be obtained on the screen is called  real image .It is always inverted .
ii)Virtual image:-The image which can not be obtained on the screen is called virtual image .It is always erect.
Uses of convex lens:-
i)It is used as magnifying lens.
ii)It is used in optical instruments i.e. Hand lens ,microscope ,telescope etc.
iii)It is used to burn paper due to its converging properties .
iv)It is used to correct long sightedness  of defect of vision.
Uses of concave lens:-It is used to correct short sightedness of defect of vision.
Parts of lens :-

 i)Principle axis :- The line passing through optical centre is called principle axis .It     is denoted by P.
ii)Optical centre :-The central point of the lens is known as optical centre .It is denoted by small c and any distance are also measured from the optical centre in the lens .
iii)Principle focus :- The point where the ray of light parallel to the principle axis converge  or diverge after refraction is called principle focus .It is denoted by F.
iv)Focal length :- The distance between the principle focus(F) and optical centre(c) is called focal length .It is denoted by f.
v)Centre of curvature :-  The centre of spherical surface from which       the lens has been cut is called centre of curvature .It is denoted by     capital C . A lens has two spherical surface or centre of curvature .
vi)2F:- Double distance of F is known as 2F .

Vii) Focusing  :-The process of adjusting distance between lens and screen in order to produce a clear image is called focusing.
Rules for drawing ray diagram  and image formed by convex and concave lens . :-
i)The ray parallel to principle axis passes through the principle focus after refraction ,but in case of concave lens the rays appear to be diverging from principle focus .

ii)The ray passing through optical center goes straight .

iii)The image is formed at that point , where these rays cut
eachother.
Position of objet and image is formed by convex lens :-
i)When object is placed at 2F =The image is formed at 2F on the other side of the lens .
ii)When object is placed beyond 2F. =The image is formed between F and 2F other side of lens .
iii)When object placed between F and 2F = The image formed beyond 2F  other side of lens .
vi)When object is placed at F = The image formed at infinity ( ) on the other side of the lens .
v) When object is at infinity ( ) = The  image is formed at F on the other side of the lens .
iv) When object is kept between principle focus (F) and optical center (C) = The image is formed beyond object  virtual, erect and larger on the same side of object .

1.)Draw neat and labeled ray diagram showing image and also write down the  characteristics of the the image are formed by convex lens .When object is placed …

 

i) Object at 2F:-

 Nature or characteristics of image :-
i)The image is formed at 2f on the other side of lens .
ii) The is real and inverted .
iii)The size of image is same to the size of object .
Uses :-The types of image is used in terrestrial  telescope .
 ii)Object at  beyond 2F:-

Nature or characteristics of image :-
i)The image is formed between F and 2F on the other side of the lens.
Ii)The image is real and inverted .
iii)The size of image is smaller or diminished than that of object .
Uses :-
I)This types of image is used in photographic camera .
 iii)Object between F and 2F :-

 Nature or characteristics of image :-
i)The is formed beyond 2F on the other side of lens .
ii)The size of the image is larger or highly magnified than that of object .
iii)The image is real and inverted .
Uses i)This types of image is used in film projector, slide projector
 iV)Object at F :-

Nature or characteristics of image :-
i)The image is at infinity (∞ ) on the other side of lens .
ii) The size of image is larger or highly magnified  that of object .
 iii)The image is real and inverted .
Uses     i)This types of image is used in the search light .
 v)Object at infinity (∞ ) :-

Nature or characteristics of image :-
i)The image  is formed at 2F .
ii)The image is real and inverted .
iii)The size of image is smaller or diminished  than that of object .
Uses :- i)This types of image is used in the telescope .
 vi)Object between F and C :-

Nature Or characteristics of image :-
i)The image is formed beyond object at same side of the lens .
ii)The size  image is larger or highly magnified than that of object .
iii)The is real and inverted .
Uses This types of image is used in the hand glass or simple microscope .
The position of  object and image is formed by concave lens  :-
i)When object is placed at 2F =                         
ii)When object is placed beyond 2F=                
iii)When object is placed between F and 2F=         
iv)When object is placed at F =                                 
v)When object is placed at infinity( )=            
vi)When object is placed between F and C=  

Nature or features of image :
i)The image is formed that of between optical centre(C)and focus(F)on same side of the lens.
ii)The image is virtual and erct .
iii) The is smaller than object.
Uses :-
i)This types of image is in the spectacles for correction of short sightedness 

1.)Draw neat and labeled ray diagram showing image and also write down the  characteristics of the the image are formed by concave lens .When object is placed …

i) Object at 2F :-.

Nature or characteristics of image
i)The image is formed between F and C at the same side of the lens .
ii)The size of  image is smaller than that of object .
iii)The image is virtual and erect .
Uses:-
i)This types of image is in the spectacles for correction of short sightedness
ii) Object at infinity ) :

Nature and characteristics of image  :-
i)The image is formed between F and C at the same side of the lens .
ii)The size of  image is smaller than that of object .
iii)The image is virtual and erect .
Uses:-
i)This types of image is in the spectacles for correction of short sightedness
 Power of lens      :-Ability of lens to converge or diverge the ray of light is called power of lens .Its S.I. unit is Dioptre (D).

Power of lens (P) =1/f (meter)               Where f = focal length

 One dioptre power :-The power of lens having   1 meter  focal length  is called one dioptre power .
Magnification   :-The ratio of image distance (v) to object distance(o) is called magnification .It have no unit .
 Magnification(M)=image distance (v) /Object distance (u)    
 Or   Image height (I) /Object height (O)          
Note:-i)if m>1 then image greater then object.
          ii) if m=1 then image is equal to object .
         iii)if m<1 then image smaller  than object.
Relation between image distance(v),object distance (u),and focal length (f):-
                1 /f = 1/u +1/v              Where f = focal length , u = object distance
and v  = image distance .
Numerical problems :-
i)Power of lens (P) = 1/f(meter)
ii) 1/f  =1 /u +1/v
1.)An object  is placed at a distance of 6 cm from focal length 4 cm
i)Calculate  focal length and nature of image ?
ii)Calculate power and nature of lens ?
iii)Calculate magnification ?
iv)Draw neat and labeled ray diagram showing image formed by convex lens.
Given,
Object distance (u)=6cm
Focal length (f)=4cm
i)by formula
  1/f  =1 /u +1/v
Or  1 /4  = 1/6    +1/v
Or   1/4   - 1/6  = 1/v
Or 1 /v    =  3-2  /12
Or    1/v   =      1/12
Therefore ,image distance (v) =12 cm
Nature of image :-
i)The image is real and inverted .
Ii)The size of image is larger than that of object .
iii)The image is formed at 12cm distance on the other side of the lens .
(Note.-If the value of v is +tive  the image is real and inverted and formed other side of the object ,but if the value of v is –tive the image is virtual and erect and same side of object.)
ii)by formula
power of lens(P) =1 /f (meter)
           or P  =   1 /4 /100    
              Or     P  =  25 D         
Therefore, thepower of lens (P) =25 Dioptre.  
The nature of lens is convex because the focal length of lens is +tive .
 iii)By formula
   Magnification (M)=  image distance (v) /object distance (u)
     Or M =    12 /6  =    2
Therefore, magnification (M) =2  or   size of image is 2 times larger than that of object.
iv)

 

2.)An object is placed 6 cm from a convex lens of focal length 2cm .
i)Calculate image distance and nature of image .
ii)Calculate power of lens .
iii) Calculate magnification .
iv)Draw neat and labeled ray diagram showing the image formed by convex lens .
3.)An object is placed at distance 2cm from a convex lens of focal length 4 cm .
i)Calculate image distance and nature of image .
ii)Draw neat and labeled ray diagram showing the image formed by convex
4.)A hand lens has 25 D power . Where should the lens be kept to read the letter of book?
Given ,
Power of lens (p) = 25D
Focal length (f) =?
By formula
P =1 /f (meter
Or 25  =   1 /f
Or f = 0.04 m
Therefore ,focal length (f) =0.04 ×100 =4cm
Hence ,the lens should be kept at 4cm for from the book.
1.)Ramita  is wearing a spectacles of power  -0.5 D .What is her defect of vision .What is focal length and what types of lens is she wearing ?
Ans. Power of lens is negative ,so lens is concave lens ,If he is concave lens so she must have short sightedness defect of vision .
Given,
Power of lens(p)=-0.5D
Focal length(f) =?
By formula
P =1 /f (meter )
Or 0.5    =
Or 0.5f   =  1
Or f  =
Therefore ,focal length of lens(f)=2m or 200cm
 Optical instruments :- The instruments which are formed by using lens are called optical instruments .They are 2 types :-
i)The optical instruments which  form real image .For example : Camera , film projector , eye  etc.
ii)The optical instruments which form virtual image .For example : Hand lens ,microscope ,telescope etc.

Uses of land lens  :-i)It is used to repair watch to see small parts  by the mechanics .
ii)It is used in the lab. to observe parts of flower ,insect etc .
 
Eye :
-The sense organ which give us sensation of sight is eye .

                                    Fig. A                                                         

                                                Fig B

Parts of eye :-



Sclera :          The strong and white color of layer of eye is called sclera . It protect and maintains the shape of eye ball .
Choroid :-The middle layer of eye is choroid .Which is rich in blood vessels
So, it help to supply blood to the retina .
Retina           :-The inner most layer of eye is called retina .It acts as a screen in which object of image is formed .
Optics  nerve  : Retina contains tiny nerve cell is called optic nerve . it help to carry massage from the of retina to the brain .                      
Ciliary muscles .-The muscles in which the lens of eye is attached is called ciliary muscles .It help to change the focal length of lens by contraction and expansion of it .
Iris :- A muscular diaphragm that remains between cornea and lens is called iris .It control the amount of light entering  to the eye by changing the diameter of pupil .
Pupil  :-The central opening of iris is called pupil . It help to pass light inside the eye .
Cornea :-The transparent protective membrane that covers the front part of eye is called cornea .
Eye lens :-A convex lens made up from transparent material present behind the iris is called eye lens. It form real ,inverted ,and smaller image than that of object .
Vitreous humour  and aqueous humour :- The vacant space behind the lens is filled with transparent liquid is called vitreous humour .
The vacant space between cornea and lens filled with transparent liquid is called aqueous humour .Aqueous humour and vitreous humour both help to maintain shape and size of eye ball .
Focusing :-The process of adjusting the distance between the and screen in order to produce image is called focusing . The focusing is done in eye by change the focal length with help of ciliary muscles .
Accommodation :-The ability of an eye to focus the distant object and far object on the retina is known as accommodation.

Far point :-The farthest point from the eye which can be seen clearly (  ) from the eye .
Near point :- The nearest point from the eye which can be seen clearly is known near point .The near point of normal human is 25cm from the eye .
Defect of vision :-When the lens of can not change its focal length according to the distance of object then eye become unable to see the object clearly placed at any point .This types defect in eye is known as defect of vision .
Types of defect of vision:- It is 2 types :
i)Long sightedness or hypermetropia .-The sightedness in which eye can see far object clearly but can not see the near object clearly is called long sightedness .
Causes of long sightedness :-

 i)The lens become to thin .
ii)The lens has long focal length .
iii)The image of near object is formed beyond retina .
Remedy or correction of long sightedness :-
Long sightedness is corrected by using spectacles containing convex lens because it converge the ray of light and help to form image of near  object on the retina .

2.)Short sightedness or myopia :- 
The sightedness in which eye can see near object clearly but for object can not see clearly is known as short sightedness .
Causes of short sightedness :-

i)The lens become to thick .
ii)The lens has short focal length .
iii)The image of far object is formed at the front of retina .
Remedy or correction of short sightedness  :-

The short sightedness is corrected by using spectacles containing concave lens because it diverge the ray of light and help to form image of far object on the retina.

Other ways of correction of defect of vision apart from using spectacles:
1.Contact Lens: A  thin, transparent plastic or glass disk that fits over the cornea of the eye to correct refractive errors or improve vision is known as contact lens.
There are two main types of contact lenses: 


i)Soft contact lens. Soft contact lenses are made of a flexible hydrogel material that allows oxygen to pass through to the cornea.
ii) Rigid contact lens :Rigid contact lenses are made of a hard plastic material that does not allow oxygen to pass through to the cornea.
It is used to correct:
i)Myopia (Near sightedness)
ii) Hypermetropia (Far sightedness)
iii)Astigmatism: Astigmatism is a common vision condition that causes blurred (Dhamilo) vision. It occurs when the cornea or lens of the eye is not evenly curved. But having a smooth, round shape like a basketball, the cornea or lens
iv)Presbyopia: Presbyopia is a common age-related vision condition that causes difficulty focusing on near objects., the lens in your eye becomes less flexible and loses its ability to change shape to focus on near .This causes near objects to appear blurry.

 Advantages of contact lenses than that of eye glasses,
i)Wider field of view: Contact lenses provide a wider field of view than eyeglasses, For example :It is useful  for people who participate in sports or other activities that require a wide range of vision.
ii)No frames: Contact lenses do not have frames.
iii)Improved appearance: Some people feel that contact lenses make them look more attractive (colourful cornea ) than eyeglasses.
Disadvantages to wearing contact lenses:
i)Cost: Contact lenses are more expensive than eyeglasses.
ii)Care and maintenance: Contact lenses require more care and maintenance than eyeglasses.
iii)Risk of infection: Contact lenses can increase the risk of eye infections.

2.Laser Eye Surgery:
 A  refractive eye surgery that uses a laser to reshape the cornea, the clear front surface of the eye to correct refractive errors i.e. nearsightedness (myopia), farsightedness (hypermertopia), and astigmatism is called Laser eye surgery.
There are main two common type of laser surgery:
i.)LASIK (laser-assisted in situ keratomileusis):In LASIK, a thin flap is created in the cornea using a femtosecond laser., then laser is used to reshape the underlying corneal tissue and  flap is then repositioned to correct refractive error.

ii.) PRK (photorefractive keratectomy): In PRK,  the thin top layer (epithelium,)of the cornea, is removed, then reshaped with an excimer laser to refractive error.

Advantages  of Laser Eye Surgery
i.)Improved vision
ii.)Reduced  dependence on glasses or contact lenses
iii.)Improved self-esteem and quality of life
Disadvantages  of Laser Eye Surgery
i.)Dry eyes
ii.)Temporary vision disturbances.
iii.)Infection
 
Other problems related to Eyes apart from defect of vision:
a)Cataract (Motibindu):
A defect  of vision in which a cloudy area is formed in the eye lens ,which can cause blurred vision(dhamilo), , and glare(Chamak)  is called  Cataract.

Causes of cataracts
i.)Aging: Cataracts are a natural part of aging because due aging  proteins in the lens of the eye break down and clump
together(cluster), causing the lens to become cloudy.
ii.)Injury: A injury  to the eye can cause a cataract to form.
iii.)Radiation: Due to Exposure to radiation, such as from X-rays or ultraviolet (UV) rays, can increase the risk of developing cataracts.
iv)Diseases: Certain diseases, such as diabetes, can increase the risk of developing cataracts.
Symptoms of cataracts
i.)Glare
ii.)Difficulty seeing in low light
iii.)Difficulty seeing colours
Remedies for cataracts
It is corrected by surgery in which the cloudy lens is  removed. During cataract surgery, the cloudy lens is removed and replaced with an artificial lens. 

Prevention of cataracts
I.)Wearing sunglasses to protect your eyes from UV rays.
ii.)Smoking.
iii.)Eating a healthy diet.
iv.)Controlling your blood sugar if you have diabetes.
 
b.)Colourblindness:
A defect of vision in which a person has defect in seeing  or identifying blue ,green and red colour is known as colour blindness. It is  also called  colour deficiency or Dalton-ism,which is named by its discoverer Johan Dalton.

Types of color blindness:
i.) Monochromacy :When 2 or 3 cones pigments (red, blue, and green) present in the eye are absent or damaged is known as monochromacy colour blindness .it is also known as total colour blindness. This is the rarest type of coluor blindness. People with total color blindness see only in shades of gray.
Causes of Monochromacy:
i.)People with monochromacy have no working cone cells, which are the cells in the eye that are responsible for colour vision
ii.) It is usually inherited, but it can also be caused by eye injury or disease.
Remedy of Monochromacy:
There is no cure for Monochromacy, but by using special glasses or contact lenses that can improve their contrast vision.

ii.)Dichromacy : When only one cones pigments (red, blue, and green) present in the eye is absent or damaged is known as  Dichromacy colour blindness .it is also known as Partial colour blindness.
The most common type of dichromacy are
i.)Red-green color blindness. People with red-green color blindness have difficulty distinguishing between red and green, and they may see these colors as shades of brown or yellow.

ii.) blue-yellow colour blindness.: People with blue-yellow color blindness have difficulty distinguishing between blue and yellow, and they may see these colors as shades of green or red.

Causes of Dichromacy colour blindness:
People with dichromacy have two working cone cells, but one of them is not functioning properly. As a result, they have difficulty distinguishing between certain colors.
Remedy:
There is no cure for dichromacy, but by using special glasses or contact lenses that can improve their color vision.
 
c.)Night Blindness: The defect of vision in which a person can see object clearly during day time but cannot see object clearly at night is called Night blindness. It is also known as nyctalopia.

Causes of night blindness
i.)Retinitis pigmentosa: This is a genetic disorder that affects the retina. Retinitis pigmentosa causes the rod cells in the retina to degenerate, which makes it difficult to see in low light.
ii.)Cataracts: This is a clouding of the lens of the eye, which can make it difficult to see in low light
iii.)Glaucoma: This is a group of eye diseases that damage the optic nerve,  Glaucoma can cause night blindness, as well as other vision problems.
iv)Vitamin A deficiency:  because vitamin A is necessary for the production of rhodopsin, a pigment that is important for vision in low light.
v.)Nearsightedness: Nearsightedness is also causes of difficulty with night vision. 
Symptoms of night blindness
i.)Difficulty seeing stars at night
ii.)Difficulty seeing  in a dark room
iii.)Difficulty driving at night
Remedies for night blindness: The correction of night blindness depends on the following causes:
i.)if night blindness is caused by retinitis pigmentosa, there is no cure, but there are treatments that can help to slow the progression of the disease.
ii.) If night blindness is caused by cataracts, surgery can usually remove the cloudy lens and restore vision.
iii.)If night blindness is caused by vitamin A deficiency, taking vitamin A supplements can usually improve vision.
 
Effects of corneal injury on vision :
Corneal injury : Any damage to the cornea,due to the variety of things, such as scratches, cuts, burns, and infections is known as corneal injury .

Effects of corneal injury on vision
i.Blurred vision.
ii. Pain. .
iii. Light sensitivity: The injured eye may be sensitive to light, making it difficult to see in bright conditions.
iv. Glare. 
v.Infection: Corneal injuries can increase the risk of infection, which can damage the cornea .
Treatment for corneal injury
i.Eye drops: Eye drops can be used to reduce pain, inflammation, and the risk of infection.
ii.Antibiotics: Antibiotics may be prescribed to prevent or treat infection.
iii.Surgery: Surgery may be necessary to repair deep cuts or perforations.


         Unit-11          Electricity and Magnetism

Electric current or electricity  :-The rate of flow charge or electrons per unit time through electric circuit is called electric current .Its S.I. unit is ampere(A) and measured by ammeter(ie large amount) or Galvanometer(ie. little amount) .
Electric current (I) =Charge (Q) / Time(t)       
 Note :-1 coulomb charge= 6.24 ×1018 electrons
1 Ampere current :- If one coulomb charge or 6.24×1018 electrons flow in one second through a electric circuit is called 1 ampere current .
Electric circuit :-A conducting path made by connecting electric source ,load ,switch with good conducting wire is called electric current .

Types of electric circuit  :-They are 2 types :

i)Closed circuit :- The circuit in which the load is functioning due continue flow of current through the circuit is called closed  circuit .
ii)Open circuit .- The circuit in which load does not function due to switch ,broken of wire, and fuse is gone off  is called open circuit .

Ammeter :-   An electrical device which is used to measure the electric current flowing through the electrical circuit is called ammeter .It is always connected series with load in circuit and denoted by A.

Voltmeter    An electrical device which is used to measure e. m. f. or potential difference is called voltmeter . It is connected parallel with load in circuit and denoted by V.
Alternating current (A.C.)  The current that change its polarity and magnitude at certain interval time is called alternating current .It can be generated from a.c. generator or dynamo. The voltage of a.c. can be increase of decrease by using transformer .

Direct current(D.C.) :-  The current that does not change its polarity and magnitude at certain interval time is called direct current .It can  be generated by cell or battery .The voltage of d.c. current can not be increase or decrease by using transformer but by changing number of cell.

Frequency of A.C. :-  The number of times of change in polarity of a.c.per second is called frequency .For example: The frequency of electricity distributed in Kathmandu is 50hz.It means that the polarity of electric current distributed in Kathmandu changes 50 times per second .
Magnetic effect of electricity :-The conversion of electrical energy into magnetic energy by passing current through a solenoid with core of soft magnetic substance is known as magnetic effect of electricity .For example : electromagnet change electrical energy into magnetic energy.

Electro-magnet :- A temporary magnet made by passing electric current through a solenoid with a core of soft magnetic substance i.e.iron is called Electro-magnet.

Methods for increasing the magnetic  power of electromagnet :-
i)By increasing the number of turns of wire in the coil .
ii)By increasing the strength of electric power .
iii)By using soft magnetic substances ie . iron inside solenoid .
Widely uses of electromagnet :- Due to following reasons electromagnet are widely used :
i)It  is a temporary magnet so magnetic properties can be increased or decreased according to our necessity or desire .
ii)The shape of the magnet can be changed according to our desire .
iii)The strength of the magnet can be changed according to needs .

Magnetic field around a current carrying straight wire:
The magnetic field around a current-carrying straight wire is a region of space where a magnetic force is exerted on moving charged particles. The magnetic field lines are concentric circles centered on the wire, with the direction of the field lines given by the right-hand thumb rule. The strength of the magnetic field is directly proportional to the magnitude of the current and inversely proportional to the distance from the wire.

The right-hand thumb rule states that if you point your right thumb in the direction of the current flow, your fingers will curl in the direction of the magnetic field lines. For example, if a current is flowing from left to right through a straight wire, the magnetic field lines will be circling the wire in a counterclockwise direction.

Magnetic Field around Solenoid :
A solenoid is a type of electromagnet that consists of a coil of wire wrapped around a cylindrical core. When an electric current is passed through the wire, a magnetic field is created inside the solenoid. The magnetic field lines inside the solenoid are parallel and uniform, and they point from the north pole to the south pole of the solenoid.

The strength of the magnetic field inside a solenoid depends on three factors:
i.The number of turns of wire in the coil
ii.The strength of the current flowing through the wire
iii.The permeability of the core material
Magnetic lines of force :-The imaginary curve drawn N-Pole to S-pole around magnet that show the direction of magnetic force is called magnetic lines of force .

Properties of magnetic lines of force :- i)They are continuous closed curves.
ii)The magnetic lines of force moves from N-Pole to S-pole .
iii)The magnetic lines of force does not intersect each other.
Magnetic flux :-Total n. of magnetic lines of force present in an area is called magnetic flux.
Electro-magnetic induction :-The process by which electric current is induced in a closed circuit due to change in magnetic flux through a closed circuit is called Electro-magnetic induction .for example: Dynamo or generator based on principle of Electro-magnetic induction.    

Induced current :-   The current produced in a conductor by electro-magnetic induction is called induced current .
Induced e.m.f. :-The electro- motive force (voltage) produced by electro-magnetic induction is called electro-motive force .
Faraday’s electro-magnetic induction  :-
i)When there is change in magnetic flux linked with closed a circuit emf is induced in the circuit .
ii)The magnitude of induced emf is directly proportional to rate of change magnetic flux .
iii)The induced emf last as long as the change in the magnetic flux.

3.)Dynamo :- An electrical device which produce electric current by the process of electric magnetic induction is called dynamo. It produce small amount of electricity .it convert  kinetic  energy into electrical energy .

Principle :- It is based on principle of electro-magnetic induction .
Working :- It consist of rotating head with a magnet Below the magnet an isolated copper wire around the soft iron is kept .This all system is sealed with an aluminum  pot .when head is rotated with help of wheel magnet also moves, due to which magnetic flux change and emf is induced in coil , that flow through the wire .

Uses  :-i)It is used to produce small amount of current electricity for operating electrical device .
 Generator :-An electrical device which produce large a amount of current electricity by process of electro- magnetic induction is called  generator .It convert kinetic energy into electrical energy .
Principle  :- it based on the principle of electro –magnetic induction .
Working :-  It consist of rectangular coil of a wire ,which is rotated between two opposite poles of strong magnet .when rectangular coli  is rotated with help of turbine due to which magnetic flux change and emf is induced in the coil .that flow through the wire .
Uses  -  It is used to produce large amount of electricity for operating industries ,factories etc. .
Methods to increase strength of dynamo or generator:-
i)By increasing the number of turns of coil .
ii) By increasing strength of the magnet .
iii) By increasing the speed of rotation of magnetic field , or by increasing the speed of rotation of coil in the magnetic field .
iv)By decreasing the distance between magnet and the coil.
Motor effect :- When current carrying conductor is kept in a magnetic field ,a movement is developed in the conductor continuously .This called motor effect .It takes place due to attraction and repulsion between external magnetic field and that of current around the wire.  For example : electric motor ,electric fan based on the principle of motor effect . 

2.)Electric motor :-An electrical device that electrical energy into kinetic energy is called electric motor .

Principle :-It based on the principle of motor effect. permanent magnet is used in electric motor .
Types of motor :-   They are two types :
i)AC motor    that is uses AC supply.ie. motor of fan ,motor of washing machine .
ii)DC motor that uses DC Supply. ie. the motor of battery operated appliances .
Construction and working .-  It consist of coils between two poles of strong magnet .When the current is passed through the coils a magnetic field is set up around it .This magnetic field interacts with the magnetic field interacts with the magnetic field of the magnet .As a result ,the coil experiences a force due to which it begin to rotates.
Uses :- i)It is used to run industries ,factories etc.
ii)It is used to run different electrical appliances .

Large-scale electric sources :The devices that generate a large amount of electricity are called Large-scale electric sources.  They are used to power large cities or industrial facilities. For example :Some common types of large-scale electric sources are:
i.)Power plants: Power plants are  devices that convert other forms of energy, such as nuclear, fossil fuel, or hydroelectric energy, into electricity. Power plants are the largest sources of electricity in the world.

ii.)Solar farms: Solar farms are large scales  of solar panels that convert sunlight into electricity. 

iii.)Wind farms: Wind farms are large scales  of wind turbines that convert wind energy into electricity. 

iv.) Geothermal power Plant :The power plants that generate electricity from heat that is extracted from the Earth's interior is called Geothermal power plants.

3.)Transformer:-  An electrical device which convert high alternating voltage into low alternating voltage and low alternating voltage into high alternating voltage is called transformer .
Principle of transformer  :-It is based on principle of of mutual induction ie. when an alternating current is passed into one coil an induced current is produced in the neighboring or adjacent coil.
Construction and working ;-  It consist of three major parts ie. soft iron core, primary coil ,and secondary coil .Soft iron core consist of rectangular frame of thin laminated sheets of soft iron .Each sheet is laminated by varnish or shellac in order to prevent from loss of current by reducing heating effect and soft iron has very high magnetic permeability so it help to concentrate magnetic line of force.
 
Primary voltage  and primary coil: The coil in which alternating current is supplied is called primary coil and the voltage supplied in primary coil is called primary voltage .  
Secondary  voltage and secondary coil :The coil in which electric current is induced is called secondary coil and the voltage of secondary coil is called secondary  voltage .
 
Input current and output current The current supplied in the transformer is called input current and the current produced from the transformer is called output current .
 
In transformer number of turns of primary coil should be about 1000 for greater efficiency and durability and prevent from heat, loss of energy ,and of short circuit .
Relation between primary coil(n1),secondary coil(n2),primary voltage(v1) and secondary voltage(v2).:
 Secondary voltage(v2 ) /Primary voltage(v1)   =Secondary coil(n2) /Primary coil(n1)
Or     v2   / v1   = n2  / n1 https://www.blogger.com/img/img-grey-rectangle.png       
 Type  of transformer :-  They are two types :

1.)Step up transformer  :-A transformer which convert low alternating voltage into high alternating voltage is called step up transformer. In step up transformer number of turns secondary coil is always more than that of number of turns of primary coil it is also used to transmit electricity for long distance . .For example: it is used in power station ,tv, computer x-ray tube, etc.

2.)Step down transformer :- A transformer which convert low altering voltage into high alternating voltage is called step down transformer .in this transformer the numbers turns of secondary coil is always less than that of number of primary coil .For example: It is used in electric appliances ie. battery charger electric bell, radio, etc.

Advantages of transformer :-
i)It help to convert high alternating voltage into low alternating voltage and low alternating voltage into high alternating voltage .
ii)It is used for long distance transmission of alternating current through aluminum wire .
Uses :-
I)Step up transformer is used for long transmission of ac through aluminum wire .
ii) Step up transformer is used in power station ,computer,tv.x-ray tube. etc.
ii)Step down transformer is used in radio ,electric bell, battery charger etc.
1.)What is meant by the rating of an electric bulb is 60 watt(j/s)?
Ans. It means that electrical bulb convert 60 j of electrical energy into heat energy and light energy per second .

Numerical problems
Formula :
i)P = I×V
ii) V =R×I
iii) V2   / V1= n2  / n1
iv)  I1V2   =  I2V1
1)In a house a heater of 1500w ,a refrigerator of 100w,a television of 80w,3 bulb of 60w each and an iron of 1000w are used .Calculate the rating of fuse in supply of 220v A.C. to run all appliances safely .
Ans. Given,
Total power of all appliances (P)=p1+p2+p3+ p4+p5
                                                 P=1500+100+80+60×3+1000
P  =  3760  watt
Voltage(V) =220v
Current (I)  =?
According to formula
I   =P/V
Or I  =  3760 /220    = 13
Therefore ,the current is  flowing in the circuit (I) =13 ampere
So the rating of fuse should be (I)  = 14 A
2.)A circuit with 220 v is supplied with fuse of 5A. How many bulbs of 100 watt can be safely used in the circuit .
Given,
Current (I)=5 A
Voltage(v)=220 v
By formula
Total power (P) =I×V
Or P =5×220
Total power (P)1100 watt
Power of bulb (P’) =100watt
For the safety of the circuit
P =P’×n
؞Number of bulb safely used (n) = P /P’   
Or                                           n  =1100 /100 =   1
4.)A transformer is  of 220 v primary voltage  has 770 turns of secondary coil will be necessary in order to produce 120 volt from that transformer ?
Ans.Given,
Primary voltage(v1) = 220 v
Primary turns  (n1)= 770
Secondary voltage (v2)= 120 v
Secondary coil(n2) =?
By formula
https://www.blogger.com/img/img-grey-rectangle.png  V2   / V1= n2  / n1
Or  120  /220  = n2 /770
n2   =120 x 770   /   220  
؞Secondary coil (n2) = 420
6.)A transformer has 240 input voltage .30A input current and 120 v out put voltage ,than calculate out put current ..
Ans. Given ,
Primary voltage(v1)= 220 v
Input current (I1)= 30A
Secondary voltage(V2)=120 v
Out put current (I2)= ?
By formula
I1V1   =   I2V2
Or 30×240  =I2×120
Or I2  =30 x 240   /120
؞Out put current (I2)=60A
7.)The number of turns in primary  winding of certain transformer is 150 times more than that in the secondary winding .Calculate the input emf in the primary winding, if the emf generated in the secondary winding is 220 v.
Ans. Given,
Number of secondary winding (n2)=X
Number of primary winding (n1)=150X
Secondary voltage (V2)=220
Primary voltage (V1) =?
By formula
V2   / V1= n2  / n1        https://www.blogger.com/img/img-grey-rectangle.png
Or  220 /v1   =x /150x
Or V1  =   220×150
؞Primary voltage (V1) =  33000 volt


















  
















































 



























 





























                                           

























 



 

























  








 






Comments

Post a Comment

Popular posts from this blog

Biology grade -9 (New Course)

Image
                                            Biology /Grade  -9 (New Course) Unit -2   (Classification of Organisms) Classification : The process of grouping    of the living being into  various groups and sub groups on the basis of similar and dissimilar characteristics  is called classification . Importance of classification : i)It makes the study of plants and  animals easier ,scientific and systematic . ii)It help the understand the  relation between various group of plants and animals . iv)It gives the ideas about  the evolution of plants and animals . v)It help to  brings uniformity in the    study of living organism  all over the world . Nomenclature : The system of providing scientific name to all the    living organism is called nomenclature . Binomial system of nomenclature : The naming of each organism by two words a generic name and specific name is known as binomial system of nomenclature .For example :scientific name  of human being is Homo sapiens  ,where  Home is the nam
Read more

Biology grade -10 (New Course)

Image
                                    Biology /Grade  -10 (New Course)                                    Unit -2   Classification of Living being Classification : The process of grouping  of the living being into  various groups and sub groups on the basis of similar and dissimilar characteristics  is called classification . Importance of classification : i)It makes the study of plants and  animals easier ,scientific and systematic . ii)It help the understand the  relation between various group of plants and animals . iv)It gives the ideas about  the evolution of plants and animals . v)It help to  brings uniformity in the  study of living organism  all over the world . Nomenclature : The system of providing scientific name to all the  living organism is called nomenclature . Binomial system of nomenclature : The naming of each organism by two words a generic name and specific name is known as binomial system of nomenclature .For example :scientific name  of human being is Homo sapiens  
Read more