Physics: Sample Solution Paper- 4, Class 12 | Physics for Grade 12 PDF Download

 Page 1


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
CBSE Board 
Class XII – Physics 
Sample Paper – 4 Solution 
 
1. The proton A and the electron B will experience electrostatic force of equal magnitude 
but in opposite direction. 
 
2. As
mv
r
qB
? , for same v and B, .
m
r
q
? Since 
m
q
 is smaller for an electron, the radius of 
the circular path followed by the electron will be smaller. 
 
3. The human eye is most sensitive for 
14
5.405 10 . Hz ? 
 
4. Induced current in the loop will be in the clockwise direction to oppose its origin. 
 
5. Since 
? ?
12
1 1 1
1 n
f R R
??
? ? ?
??
??
 
Taking 
? ?
12
21
1
,,
n
R R R R
fR
?
? ? ? ?    …. (1)  
When lens is cut, then 
12
11
,,
'
n
R R R
fR
?
? ? ? ?  …..(2)  
Using equation (1) and equation (2), we get 
' 2 60 f f cm ?? 
 
6. No, matter waves are not electromagnetic waves.  
The de Broglie wave equation is ? ?
h
mv
  
 
7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor 
conducts either ways. Hence, a transistor cannot be used as a rectifier. 
 
8. The negative energy of the electron orbiting around nucleus keeps it bounded with the 
nucleus. If the energy of the electron becomes positive, the electron will no longer be 
bounded with the nucleus. 
 
 
 
 
 
 
Page 2


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
CBSE Board 
Class XII – Physics 
Sample Paper – 4 Solution 
 
1. The proton A and the electron B will experience electrostatic force of equal magnitude 
but in opposite direction. 
 
2. As
mv
r
qB
? , for same v and B, .
m
r
q
? Since 
m
q
 is smaller for an electron, the radius of 
the circular path followed by the electron will be smaller. 
 
3. The human eye is most sensitive for 
14
5.405 10 . Hz ? 
 
4. Induced current in the loop will be in the clockwise direction to oppose its origin. 
 
5. Since 
? ?
12
1 1 1
1 n
f R R
??
? ? ?
??
??
 
Taking 
? ?
12
21
1
,,
n
R R R R
fR
?
? ? ? ?    …. (1)  
When lens is cut, then 
12
11
,,
'
n
R R R
fR
?
? ? ? ?  …..(2)  
Using equation (1) and equation (2), we get 
' 2 60 f f cm ?? 
 
6. No, matter waves are not electromagnetic waves.  
The de Broglie wave equation is ? ?
h
mv
  
 
7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor 
conducts either ways. Hence, a transistor cannot be used as a rectifier. 
 
8. The negative energy of the electron orbiting around nucleus keeps it bounded with the 
nucleus. If the energy of the electron becomes positive, the electron will no longer be 
bounded with the nucleus. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
9.  
(i) water ? ?
2
HO   
(ii) oxygen ? ?
2
O 
The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric 
constant for the medium.  
 
10. Resistance = 
A
?  
 
2
4
dr
dR
r
?
?
?   
 
           ?  Total resistance 
2
2
2
1
1
1
44
r
r
r
r
dr
rr
??
??
??
? ? ?
??
??
?
 
             
12
11
4
R
rr
?
?
??
??
??
??
  
 
11. When current flows through a solenoid, it flows in same direction in each turn as shown 
in the figure below. As current through each turn is in same direction, they attract each 
other.  
 
           Hence, the solenoid contracts in length. 
 
 
 
 
 
Page 3


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
CBSE Board 
Class XII – Physics 
Sample Paper – 4 Solution 
 
1. The proton A and the electron B will experience electrostatic force of equal magnitude 
but in opposite direction. 
 
2. As
mv
r
qB
? , for same v and B, .
m
r
q
? Since 
m
q
 is smaller for an electron, the radius of 
the circular path followed by the electron will be smaller. 
 
3. The human eye is most sensitive for 
14
5.405 10 . Hz ? 
 
4. Induced current in the loop will be in the clockwise direction to oppose its origin. 
 
5. Since 
? ?
12
1 1 1
1 n
f R R
??
? ? ?
??
??
 
Taking 
? ?
12
21
1
,,
n
R R R R
fR
?
? ? ? ?    …. (1)  
When lens is cut, then 
12
11
,,
'
n
R R R
fR
?
? ? ? ?  …..(2)  
Using equation (1) and equation (2), we get 
' 2 60 f f cm ?? 
 
6. No, matter waves are not electromagnetic waves.  
The de Broglie wave equation is ? ?
h
mv
  
 
7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor 
conducts either ways. Hence, a transistor cannot be used as a rectifier. 
 
8. The negative energy of the electron orbiting around nucleus keeps it bounded with the 
nucleus. If the energy of the electron becomes positive, the electron will no longer be 
bounded with the nucleus. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
9.  
(i) water ? ?
2
HO   
(ii) oxygen ? ?
2
O 
The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric 
constant for the medium.  
 
10. Resistance = 
A
?  
 
2
4
dr
dR
r
?
?
?   
 
           ?  Total resistance 
2
2
2
1
1
1
44
r
r
r
r
dr
rr
??
??
??
? ? ?
??
??
?
 
             
12
11
4
R
rr
?
?
??
??
??
??
  
 
11. When current flows through a solenoid, it flows in same direction in each turn as shown 
in the figure below. As current through each turn is in same direction, they attract each 
other.  
 
           Hence, the solenoid contracts in length. 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: 
           or
dI E
E L dI dt
dt L
??  
 
00
sin
or sin
E t dt E
dI I t dt
LL
?
? ??
?
 
 
0
cos
E
It
L
?
?
??      
            
0
or  sin
2
??
??
??
?
? I I t     
              Where 
0
0
E
I
L ?
? 
 
13. Here 
1 2 2
100 , 10 , 20 q q C r cm r cm ? ? ? ? ?  
        Work done is 
         
1 2 2 1
0 1 2
4
?? ?
?
??
??
??
qq r r
W
rr
     
               
? ?
2
69
2
10 1
100 10 9 10
200 10
?
?
??
? ? ? ? ?
??
??
  
  450 J ?     
 
14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the 
circuit. This large induced e.m.f. across the gap causes sparking in the switch.  
 
OR 
 
Iron bar experiences a retarding force. It means eddy currents are there, which are 
produced whenever there is a change in magnetic flux. So we conclude that iron bar is a 
magnet. 
 
15. A stationary charge produces only an electric field around it. When a charge moves with 
a constant velocity it produces a constant magnetic field in addition to the electric field. 
As the charge is accelerated, both electric and magnetic fields change with time and 
space. One becomes the source of the other, thus giving electromagnetic waves. 
 
 
 
 
 
 
Page 4


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
CBSE Board 
Class XII – Physics 
Sample Paper – 4 Solution 
 
1. The proton A and the electron B will experience electrostatic force of equal magnitude 
but in opposite direction. 
 
2. As
mv
r
qB
? , for same v and B, .
m
r
q
? Since 
m
q
 is smaller for an electron, the radius of 
the circular path followed by the electron will be smaller. 
 
3. The human eye is most sensitive for 
14
5.405 10 . Hz ? 
 
4. Induced current in the loop will be in the clockwise direction to oppose its origin. 
 
5. Since 
? ?
12
1 1 1
1 n
f R R
??
? ? ?
??
??
 
Taking 
? ?
12
21
1
,,
n
R R R R
fR
?
? ? ? ?    …. (1)  
When lens is cut, then 
12
11
,,
'
n
R R R
fR
?
? ? ? ?  …..(2)  
Using equation (1) and equation (2), we get 
' 2 60 f f cm ?? 
 
6. No, matter waves are not electromagnetic waves.  
The de Broglie wave equation is ? ?
h
mv
  
 
7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor 
conducts either ways. Hence, a transistor cannot be used as a rectifier. 
 
8. The negative energy of the electron orbiting around nucleus keeps it bounded with the 
nucleus. If the energy of the electron becomes positive, the electron will no longer be 
bounded with the nucleus. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
9.  
(i) water ? ?
2
HO   
(ii) oxygen ? ?
2
O 
The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric 
constant for the medium.  
 
10. Resistance = 
A
?  
 
2
4
dr
dR
r
?
?
?   
 
           ?  Total resistance 
2
2
2
1
1
1
44
r
r
r
r
dr
rr
??
??
??
? ? ?
??
??
?
 
             
12
11
4
R
rr
?
?
??
??
??
??
  
 
11. When current flows through a solenoid, it flows in same direction in each turn as shown 
in the figure below. As current through each turn is in same direction, they attract each 
other.  
 
           Hence, the solenoid contracts in length. 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: 
           or
dI E
E L dI dt
dt L
??  
 
00
sin
or sin
E t dt E
dI I t dt
LL
?
? ??
?
 
 
0
cos
E
It
L
?
?
??      
            
0
or  sin
2
??
??
??
?
? I I t     
              Where 
0
0
E
I
L ?
? 
 
13. Here 
1 2 2
100 , 10 , 20 q q C r cm r cm ? ? ? ? ?  
        Work done is 
         
1 2 2 1
0 1 2
4
?? ?
?
??
??
??
qq r r
W
rr
     
               
? ?
2
69
2
10 1
100 10 9 10
200 10
?
?
??
? ? ? ? ?
??
??
  
  450 J ?     
 
14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the 
circuit. This large induced e.m.f. across the gap causes sparking in the switch.  
 
OR 
 
Iron bar experiences a retarding force. It means eddy currents are there, which are 
produced whenever there is a change in magnetic flux. So we conclude that iron bar is a 
magnet. 
 
15. A stationary charge produces only an electric field around it. When a charge moves with 
a constant velocity it produces a constant magnetic field in addition to the electric field. 
As the charge is accelerated, both electric and magnetic fields change with time and 
space. One becomes the source of the other, thus giving electromagnetic waves. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
16. Image of the object is formed at focus of objective. This image acts like an object for 
virtual image of
1
L . Now virtual image produced by 
1
L should be located at the focus of                    
2
. L   
       Since 
12
2 /3 L L f ? 
       Image distance from 
1
is /3 L v f ??  
       
1 1 1
f v u
? ? ?  
        
1 3 1
f f u
? ? ? 
               /4 uf ? ? ?  
17.  
(i) Actual depth t =12.5 cm  
Apparent depth a = 9.4 cm 
12.5
1.33
9.4
aw
t
a
? ? ? ?  
(ii)  1.63
al
? ?   
12.5
7.7
1.63
l
al
t
a cm
?
? ? ?  
Therefore, the microscope has to be moved by ? ? 9.4 7.7 , cm ? i.e., 1.7 cm  
 
18. The capacitor can be considered as split into two capacitors in series as shown below 
 
 Here, 
1 2 0
12
22
o
K A k A
c and c
dd
??
??  
 The capacitance of capacitors in series is 
  
12
1 1 1
c c c
??    
               
12
12
cc
c
cc
??
?
  
  
12
12
2
o
A kk
c
d k k
???
?
??
?
??
  
Page 5


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
CBSE Board 
Class XII – Physics 
Sample Paper – 4 Solution 
 
1. The proton A and the electron B will experience electrostatic force of equal magnitude 
but in opposite direction. 
 
2. As
mv
r
qB
? , for same v and B, .
m
r
q
? Since 
m
q
 is smaller for an electron, the radius of 
the circular path followed by the electron will be smaller. 
 
3. The human eye is most sensitive for 
14
5.405 10 . Hz ? 
 
4. Induced current in the loop will be in the clockwise direction to oppose its origin. 
 
5. Since 
? ?
12
1 1 1
1 n
f R R
??
? ? ?
??
??
 
Taking 
? ?
12
21
1
,,
n
R R R R
fR
?
? ? ? ?    …. (1)  
When lens is cut, then 
12
11
,,
'
n
R R R
fR
?
? ? ? ?  …..(2)  
Using equation (1) and equation (2), we get 
' 2 60 f f cm ?? 
 
6. No, matter waves are not electromagnetic waves.  
The de Broglie wave equation is ? ?
h
mv
  
 
7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor 
conducts either ways. Hence, a transistor cannot be used as a rectifier. 
 
8. The negative energy of the electron orbiting around nucleus keeps it bounded with the 
nucleus. If the energy of the electron becomes positive, the electron will no longer be 
bounded with the nucleus. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
9.  
(i) water ? ?
2
HO   
(ii) oxygen ? ?
2
O 
The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric 
constant for the medium.  
 
10. Resistance = 
A
?  
 
2
4
dr
dR
r
?
?
?   
 
           ?  Total resistance 
2
2
2
1
1
1
44
r
r
r
r
dr
rr
??
??
??
? ? ?
??
??
?
 
             
12
11
4
R
rr
?
?
??
??
??
??
  
 
11. When current flows through a solenoid, it flows in same direction in each turn as shown 
in the figure below. As current through each turn is in same direction, they attract each 
other.  
 
           Hence, the solenoid contracts in length. 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: 
           or
dI E
E L dI dt
dt L
??  
 
00
sin
or sin
E t dt E
dI I t dt
LL
?
? ??
?
 
 
0
cos
E
It
L
?
?
??      
            
0
or  sin
2
??
??
??
?
? I I t     
              Where 
0
0
E
I
L ?
? 
 
13. Here 
1 2 2
100 , 10 , 20 q q C r cm r cm ? ? ? ? ?  
        Work done is 
         
1 2 2 1
0 1 2
4
?? ?
?
??
??
??
qq r r
W
rr
     
               
? ?
2
69
2
10 1
100 10 9 10
200 10
?
?
??
? ? ? ? ?
??
??
  
  450 J ?     
 
14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the 
circuit. This large induced e.m.f. across the gap causes sparking in the switch.  
 
OR 
 
Iron bar experiences a retarding force. It means eddy currents are there, which are 
produced whenever there is a change in magnetic flux. So we conclude that iron bar is a 
magnet. 
 
15. A stationary charge produces only an electric field around it. When a charge moves with 
a constant velocity it produces a constant magnetic field in addition to the electric field. 
As the charge is accelerated, both electric and magnetic fields change with time and 
space. One becomes the source of the other, thus giving electromagnetic waves. 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
16. Image of the object is formed at focus of objective. This image acts like an object for 
virtual image of
1
L . Now virtual image produced by 
1
L should be located at the focus of                    
2
. L   
       Since 
12
2 /3 L L f ? 
       Image distance from 
1
is /3 L v f ??  
       
1 1 1
f v u
? ? ?  
        
1 3 1
f f u
? ? ? 
               /4 uf ? ? ?  
17.  
(i) Actual depth t =12.5 cm  
Apparent depth a = 9.4 cm 
12.5
1.33
9.4
aw
t
a
? ? ? ?  
(ii)  1.63
al
? ?   
12.5
7.7
1.63
l
al
t
a cm
?
? ? ?  
Therefore, the microscope has to be moved by ? ? 9.4 7.7 , cm ? i.e., 1.7 cm  
 
18. The capacitor can be considered as split into two capacitors in series as shown below 
 
 Here, 
1 2 0
12
22
o
K A k A
c and c
dd
??
??  
 The capacitance of capacitors in series is 
  
12
1 1 1
c c c
??    
               
12
12
cc
c
cc
??
?
  
  
12
12
2
o
A kk
c
d k k
???
?
??
?
??
  
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 4 Solution 
 
     
OR 
Let ? be the surface charge density of capacitor plates of area A. Electric field          
between the plates in the air space is 
 
o
o
E
?
?
?    
 
           As in case of conducting slab ?
po
EE net electric field inside the conducting slab is 
            zero. 
           Now potential difference between the plates of capacitor is 
             
? ? ? ?
o
o
V E d t d t
?
?
? ? ? ?   
              QA ? ? 
             
1/
oo
AC Q
C
V d t t d
?
? ? ?
??
 
             Where 
o
o
EA
C
d
?  
 
19. Since 100 ? ? 
 
3
2 10 A
?; ?; ?
?
??
? ? ?
c
CE BE BC
I
V V V