CBSE Physics Past year paper (Solutions) - 2019, Class 12 Class 12 Notes | EduRev

Physics Class 12

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Class 12 : CBSE Physics Past year paper (Solutions) - 2019, Class 12 Class 12 Notes | EduRev

 Page 1


  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
CBSE 
Class XII Physics 
Board Paper – 2019 Solution 
 
SECTION – A  
1. Plot of resistivity versus temperature for a typical semiconductor: 
 
 
2. Attenuation: The loss of strength of a signal propagating through a medium is known 
as attenuation. 
 
3. Sphere A will be negatively charged and sphere B will be positively charged. 
OR 
As the negatively charged rod is brought near the metallic sphere, the positive charges 
accumulate at the near end and the electron moves towards the farther end. When we 
earth the sphere, the electrons flow to the ground and the sphere becomes positively 
charged. 
 
4.  
 
? ?
? ? ?
?
? ? ?
? ? ?
?
? ? ?
? ? ? ? ?
?
? ? ?
?
??
? ? ?
new
new
new
new
h KE
KE 2h
2h
KE
h
2h
KE
h
KE 2
h
 
If the frequency of incident radiation doubles, the new kinetic energy will be more than 
double. 
 
Page 2


  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
CBSE 
Class XII Physics 
Board Paper – 2019 Solution 
 
SECTION – A  
1. Plot of resistivity versus temperature for a typical semiconductor: 
 
 
2. Attenuation: The loss of strength of a signal propagating through a medium is known 
as attenuation. 
 
3. Sphere A will be negatively charged and sphere B will be positively charged. 
OR 
As the negatively charged rod is brought near the metallic sphere, the positive charges 
accumulate at the near end and the electron moves towards the farther end. When we 
earth the sphere, the electrons flow to the ground and the sphere becomes positively 
charged. 
 
4.  
 
? ?
? ? ?
?
? ? ?
? ? ?
?
? ? ?
? ? ? ? ?
?
? ? ?
?
??
? ? ?
new
new
new
new
h KE
KE 2h
2h
KE
h
2h
KE
h
KE 2
h
 
If the frequency of incident radiation doubles, the new kinetic energy will be more than 
double. 
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
5.  
?
0
e
0e
f
m
f
on increasing f and decreasing f we can produce large 
magnification
 
OR 
? ? D= 1
1
 
And hence angle of minimum deviation also decreases.
A
As
?
?
?
?
? 
 
SECTION – B  
6.  
 
 
After reflection from a convex mirror, the rays are diverging in nature and hence will 
never meet. Therefore, the convex mirror always gives a virtual and erect image. 
 
7.  
Fission Fusion 
When neutrons are bombarded on a 
heavy nucleus, it splits into two nearly 
equal light fragments. 
At very high temperature and pressure, 
two light nuclei combine to form a heavy 
nucleus. 
Possible at ordinary temperature and 
pressure. 
Possible at very high temperature and 
pressure. 
Example: 
1 235 144 89 1
0 92 56 36 0
n+ U 3 Ba Kr n ? ? ? Example:
1 1 2
1 1 1
0.42 H H H e v MeV
?
? ? ? ? ? 
 
 
8. When an electron makes a transition from the second excited state to the first excited 
state: 
Page 3


  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
CBSE 
Class XII Physics 
Board Paper – 2019 Solution 
 
SECTION – A  
1. Plot of resistivity versus temperature for a typical semiconductor: 
 
 
2. Attenuation: The loss of strength of a signal propagating through a medium is known 
as attenuation. 
 
3. Sphere A will be negatively charged and sphere B will be positively charged. 
OR 
As the negatively charged rod is brought near the metallic sphere, the positive charges 
accumulate at the near end and the electron moves towards the farther end. When we 
earth the sphere, the electrons flow to the ground and the sphere becomes positively 
charged. 
 
4.  
 
? ?
? ? ?
?
? ? ?
? ? ?
?
? ? ?
? ? ? ? ?
?
? ? ?
?
??
? ? ?
new
new
new
new
h KE
KE 2h
2h
KE
h
2h
KE
h
KE 2
h
 
If the frequency of incident radiation doubles, the new kinetic energy will be more than 
double. 
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
5.  
?
0
e
0e
f
m
f
on increasing f and decreasing f we can produce large 
magnification
 
OR 
? ? D= 1
1
 
And hence angle of minimum deviation also decreases.
A
As
?
?
?
?
? 
 
SECTION – B  
6.  
 
 
After reflection from a convex mirror, the rays are diverging in nature and hence will 
never meet. Therefore, the convex mirror always gives a virtual and erect image. 
 
7.  
Fission Fusion 
When neutrons are bombarded on a 
heavy nucleus, it splits into two nearly 
equal light fragments. 
At very high temperature and pressure, 
two light nuclei combine to form a heavy 
nucleus. 
Possible at ordinary temperature and 
pressure. 
Possible at very high temperature and 
pressure. 
Example: 
1 235 144 89 1
0 92 56 36 0
n+ U 3 Ba Kr n ? ? ? Example:
1 1 2
1 1 1
0.42 H H H e v MeV
?
? ? ? ? ? 
 
 
8. When an electron makes a transition from the second excited state to the first excited 
state: 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
??
??
??
?
??
2
1
The wavelength of the emitted radiation when electron
makes a transition from 2nd excited state to 1st  excitded state
1 1 1
RZ
49
When electron makes transition from 1st excited state to
ground st
??
??
??
?
??
?
?
?
2
2
1
2
ate
1 1 1
RZ 
14
on solving 
27
5
 
 
9. Because of symmetry, the forces
14
 and F F ,
25
 and F F will cancel out each other and the 
effective force acting on the charge q ? would be
3
F . 
  
2
3 2
kq
F
l
? 
OR 
 
 
 
2
2
2
t=-qElsin?
t=Ia
ml a=-qElsin?
-qElsin?
a=
ml
-qE?
a=
ml
-qE?
-? ?=
ml
qE
?=
ml
ml
T=2p
qE
 
Page 4


  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
CBSE 
Class XII Physics 
Board Paper – 2019 Solution 
 
SECTION – A  
1. Plot of resistivity versus temperature for a typical semiconductor: 
 
 
2. Attenuation: The loss of strength of a signal propagating through a medium is known 
as attenuation. 
 
3. Sphere A will be negatively charged and sphere B will be positively charged. 
OR 
As the negatively charged rod is brought near the metallic sphere, the positive charges 
accumulate at the near end and the electron moves towards the farther end. When we 
earth the sphere, the electrons flow to the ground and the sphere becomes positively 
charged. 
 
4.  
 
? ?
? ? ?
?
? ? ?
? ? ?
?
? ? ?
? ? ? ? ?
?
? ? ?
?
??
? ? ?
new
new
new
new
h KE
KE 2h
2h
KE
h
2h
KE
h
KE 2
h
 
If the frequency of incident radiation doubles, the new kinetic energy will be more than 
double. 
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
5.  
?
0
e
0e
f
m
f
on increasing f and decreasing f we can produce large 
magnification
 
OR 
? ? D= 1
1
 
And hence angle of minimum deviation also decreases.
A
As
?
?
?
?
? 
 
SECTION – B  
6.  
 
 
After reflection from a convex mirror, the rays are diverging in nature and hence will 
never meet. Therefore, the convex mirror always gives a virtual and erect image. 
 
7.  
Fission Fusion 
When neutrons are bombarded on a 
heavy nucleus, it splits into two nearly 
equal light fragments. 
At very high temperature and pressure, 
two light nuclei combine to form a heavy 
nucleus. 
Possible at ordinary temperature and 
pressure. 
Possible at very high temperature and 
pressure. 
Example: 
1 235 144 89 1
0 92 56 36 0
n+ U 3 Ba Kr n ? ? ? Example:
1 1 2
1 1 1
0.42 H H H e v MeV
?
? ? ? ? ? 
 
 
8. When an electron makes a transition from the second excited state to the first excited 
state: 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
??
??
??
?
??
2
1
The wavelength of the emitted radiation when electron
makes a transition from 2nd excited state to 1st  excitded state
1 1 1
RZ
49
When electron makes transition from 1st excited state to
ground st
??
??
??
?
??
?
?
?
2
2
1
2
ate
1 1 1
RZ 
14
on solving 
27
5
 
 
9. Because of symmetry, the forces
14
 and F F ,
25
 and F F will cancel out each other and the 
effective force acting on the charge q ? would be
3
F . 
  
2
3 2
kq
F
l
? 
OR 
 
 
 
2
2
2
t=-qElsin?
t=Ia
ml a=-qElsin?
-qElsin?
a=
ml
-qE?
a=
ml
-qE?
-? ?=
ml
qE
?=
ml
ml
T=2p
qE
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
10.  
    
Time taken by the particle to reduce to half of the initial number is half-life. 
Time taken by the particle to reduce to 0.37 of its initial value is called average life. 
 
11.  
 
?
??
?
??
?
? ? ? ?
?
? ? ?
? ? ? ? ? ? ?
? ? ?
2 4 2
0
0
0
74
7
No of turns per unit length=10/cm=1000/m
Area of cross section=1cm 1 10 m
change in current=2-1=1A
time taken=0.1seconds
B= ni
BA niA
d di
emf nA
dt dt
1
emf 4 10 1000 1 10
0.1
emf 4 10 Wb
 
OR 
?
?
??
? ? ? ? ?
? ? ?
4
3
NBA
140 0.09 5 10
6.3 10 Wb
 
 
12.  
 
Page 5


  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
CBSE 
Class XII Physics 
Board Paper – 2019 Solution 
 
SECTION – A  
1. Plot of resistivity versus temperature for a typical semiconductor: 
 
 
2. Attenuation: The loss of strength of a signal propagating through a medium is known 
as attenuation. 
 
3. Sphere A will be negatively charged and sphere B will be positively charged. 
OR 
As the negatively charged rod is brought near the metallic sphere, the positive charges 
accumulate at the near end and the electron moves towards the farther end. When we 
earth the sphere, the electrons flow to the ground and the sphere becomes positively 
charged. 
 
4.  
 
? ?
? ? ?
?
? ? ?
? ? ?
?
? ? ?
? ? ? ? ?
?
? ? ?
?
??
? ? ?
new
new
new
new
h KE
KE 2h
2h
KE
h
2h
KE
h
KE 2
h
 
If the frequency of incident radiation doubles, the new kinetic energy will be more than 
double. 
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
5.  
?
0
e
0e
f
m
f
on increasing f and decreasing f we can produce large 
magnification
 
OR 
? ? D= 1
1
 
And hence angle of minimum deviation also decreases.
A
As
?
?
?
?
? 
 
SECTION – B  
6.  
 
 
After reflection from a convex mirror, the rays are diverging in nature and hence will 
never meet. Therefore, the convex mirror always gives a virtual and erect image. 
 
7.  
Fission Fusion 
When neutrons are bombarded on a 
heavy nucleus, it splits into two nearly 
equal light fragments. 
At very high temperature and pressure, 
two light nuclei combine to form a heavy 
nucleus. 
Possible at ordinary temperature and 
pressure. 
Possible at very high temperature and 
pressure. 
Example: 
1 235 144 89 1
0 92 56 36 0
n+ U 3 Ba Kr n ? ? ? Example:
1 1 2
1 1 1
0.42 H H H e v MeV
?
? ? ? ? ? 
 
 
8. When an electron makes a transition from the second excited state to the first excited 
state: 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
??
??
??
?
??
2
1
The wavelength of the emitted radiation when electron
makes a transition from 2nd excited state to 1st  excitded state
1 1 1
RZ
49
When electron makes transition from 1st excited state to
ground st
??
??
??
?
??
?
?
?
2
2
1
2
ate
1 1 1
RZ 
14
on solving 
27
5
 
 
9. Because of symmetry, the forces
14
 and F F ,
25
 and F F will cancel out each other and the 
effective force acting on the charge q ? would be
3
F . 
  
2
3 2
kq
F
l
? 
OR 
 
 
 
2
2
2
t=-qElsin?
t=Ia
ml a=-qElsin?
-qElsin?
a=
ml
-qE?
a=
ml
-qE?
-? ?=
ml
qE
?=
ml
ml
T=2p
qE
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
10.  
    
Time taken by the particle to reduce to half of the initial number is half-life. 
Time taken by the particle to reduce to 0.37 of its initial value is called average life. 
 
11.  
 
?
??
?
??
?
? ? ? ?
?
? ? ?
? ? ? ? ? ? ?
? ? ?
2 4 2
0
0
0
74
7
No of turns per unit length=10/cm=1000/m
Area of cross section=1cm 1 10 m
change in current=2-1=1A
time taken=0.1seconds
B= ni
BA niA
d di
emf nA
dt dt
1
emf 4 10 1000 1 10
0.1
emf 4 10 Wb
 
OR 
?
?
??
? ? ? ? ?
? ? ?
4
3
NBA
140 0.09 5 10
6.3 10 Wb
 
 
12.  
 
  
 
CBSE XII  | PHYSICS 
Board Paper – 2019 Solution 
 
     
 Effective capacitance of both 3 F ? capacitors is 6 F ? and that for ?? 1 F and 2 F
capacitors is ? 3F . Effective capacitance of the entire circuit 4 F ? . 
Energy stored is given by 
2
2
CV
 
? ?
??
2
4
4 100
2
2 10 J
0.02J
 
 
SECTION – C  
13. Effective resistance of the circuit is 8 ?. 
V = 16 V 
V=IR
16=I×8
I=2A
current in the each branch
is 1A
so potential difference across 4O is given by
V=1×4=4V
 
 
14. When the capacitor is connected to the battery, the charges starts accumulating on the 
plates of the capacitor. This process continues till the potential of the battery becomes 
equal to the battery. Because of this flow of charges the galvanometer shows 
deflection. 
E
00
1 Q Q
F = E A= A=
e A e
 
If charge Q on the capacitor changes with time, there is a current 
dQ
i
dt
? 
??
??
??
??
??
E
00
dF d Q 1 dQ
dt dt dt
 
??
? ? ?
??
??
E
d0
dF
i
dt
 
where 
d
I is the conduction current 
 
 
 
 
 
 
 
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