Physics: Sample Question Paper- 3, Class 12 | Physics for Grade 12 PDF Download

 Page 1


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
CBSE Board 
Class XII Physics 
Sample Paper - 3 
 
Time:  Three Hours Maximum Marks: 70 
 
General Instructions 
(a) All questions are compulsory. 
(b) There are 29 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 
16 carry two marks each, questions 17 to 25 carry three marks each and questions 
27 to 29 carry five marks each. 
(c) Question 26 is a value based question carrying four marks. 
(d) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each. You have to attempt only one of the given choices in such questions. 
(e) Use of calculator is not permitted. 
(f) You may use the following physical constants wherever necessary. 
-1
-1
-1
19
8
34
7
23
23
27
 C
 m s
 J s
 T ma
 J K
 /mole
 kg
1.6 10
3 10
6.6 10
4 10
1.38 10
6.023 10
1.6 10
?
?
?
?
??
??
??
??
??
??
??
o
B
A
n
e
c
h
K
N
m
?? 
 
 
1. Is the force acting between two point electric charges q 1 and q 2 kept at some distance 
apart in air, attractive or repulsive when (i) q 1q 2 > 0 (ii) q 1q 2 < 0 ?    (1) 
 
2. On a graph show the stopping potential for a given photosensitive surface varying with 
the frequencies n 1 and n 2 of incident radiations where n 1 >n 2. Given that intensity is 
same for both light radiations.   (1) 
 
3. A message signal of frequency 10 kHz is used to modulate a carrier of frequency 1 MHz. 
Find the side bands produced.  (1) 
 
 
Page 2


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
CBSE Board 
Class XII Physics 
Sample Paper - 3 
 
Time:  Three Hours Maximum Marks: 70 
 
General Instructions 
(a) All questions are compulsory. 
(b) There are 29 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 
16 carry two marks each, questions 17 to 25 carry three marks each and questions 
27 to 29 carry five marks each. 
(c) Question 26 is a value based question carrying four marks. 
(d) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each. You have to attempt only one of the given choices in such questions. 
(e) Use of calculator is not permitted. 
(f) You may use the following physical constants wherever necessary. 
-1
-1
-1
19
8
34
7
23
23
27
 C
 m s
 J s
 T ma
 J K
 /mole
 kg
1.6 10
3 10
6.6 10
4 10
1.38 10
6.023 10
1.6 10
?
?
?
?
??
??
??
??
??
??
??
o
B
A
n
e
c
h
K
N
m
?? 
 
 
1. Is the force acting between two point electric charges q 1 and q 2 kept at some distance 
apart in air, attractive or repulsive when (i) q 1q 2 > 0 (ii) q 1q 2 < 0 ?    (1) 
 
2. On a graph show the stopping potential for a given photosensitive surface varying with 
the frequencies n 1 and n 2 of incident radiations where n 1 >n 2. Given that intensity is 
same for both light radiations.   (1) 
 
3. A message signal of frequency 10 kHz is used to modulate a carrier of frequency 1 MHz. 
Find the side bands produced.  (1) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
4. Is the diode in the following circuit forward biased or reverse biased? Give reason for 
your answer.  
 (1) 
 
5. What is the frequency range of signals that are transmitted using optical fibres?  (1) 
 
6. A spherical Gaussian surface encloses charges q 1 and q 2 with                    
66
12
8.85 10 and q = - 8.85 10
??
? ? ? q C C 
(i) Calculate the electric flux passing through the surface.  
(ii) How would the flux change if the spherical Gaussian surface is replaced with a 
cubical Gaussian surface and why?  (1) 
 
7. For a given thermocouple, the emf generated across its ends is given by E = at + bt
2
 
where t in °C is the temperature of the hot junction, the cold junction being at 0 °C. If a = 
10 mV /°C and b = -0.02 mV/°C
2
, calculate the value of inversion temperature in °C.  (1) 
 
8. A 3.0 V battery is connected to an ammeter and a resistor of 3 ohms in series with it. 
What is the value of the current if the ammeter used is a galvanometer with a resistance 
of 60 ohm?  (1) 
 
9. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. 
mains. The bulb glows with some brightness. How will the glow of the bulb be affected 
on introducing a dielectric slab between the plates of the capacitor? Give reasons in 
support of your answer.  (2) 
 
10. Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two 
crossed Polaroids.  (2) 
 
11. Why is NAND gate called a universal gate. How can it to be used to realize a basic OR 
gate?  (2) 
 
12. What is modulation? What are the different types of modulation?  (2) 
 
13. Nuclear density of hydrogen is 2.3x10
17
 kg/
 
m
3
. Given A = 56 for iron, find its nuclear 
density.  (2) 
 
14. Distinguish between frequency modulation and amplitude modulation.  (2) 
 
 
 
Page 3


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
CBSE Board 
Class XII Physics 
Sample Paper - 3 
 
Time:  Three Hours Maximum Marks: 70 
 
General Instructions 
(a) All questions are compulsory. 
(b) There are 29 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 
16 carry two marks each, questions 17 to 25 carry three marks each and questions 
27 to 29 carry five marks each. 
(c) Question 26 is a value based question carrying four marks. 
(d) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each. You have to attempt only one of the given choices in such questions. 
(e) Use of calculator is not permitted. 
(f) You may use the following physical constants wherever necessary. 
-1
-1
-1
19
8
34
7
23
23
27
 C
 m s
 J s
 T ma
 J K
 /mole
 kg
1.6 10
3 10
6.6 10
4 10
1.38 10
6.023 10
1.6 10
?
?
?
?
??
??
??
??
??
??
??
o
B
A
n
e
c
h
K
N
m
?? 
 
 
1. Is the force acting between two point electric charges q 1 and q 2 kept at some distance 
apart in air, attractive or repulsive when (i) q 1q 2 > 0 (ii) q 1q 2 < 0 ?    (1) 
 
2. On a graph show the stopping potential for a given photosensitive surface varying with 
the frequencies n 1 and n 2 of incident radiations where n 1 >n 2. Given that intensity is 
same for both light radiations.   (1) 
 
3. A message signal of frequency 10 kHz is used to modulate a carrier of frequency 1 MHz. 
Find the side bands produced.  (1) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
4. Is the diode in the following circuit forward biased or reverse biased? Give reason for 
your answer.  
 (1) 
 
5. What is the frequency range of signals that are transmitted using optical fibres?  (1) 
 
6. A spherical Gaussian surface encloses charges q 1 and q 2 with                    
66
12
8.85 10 and q = - 8.85 10
??
? ? ? q C C 
(i) Calculate the electric flux passing through the surface.  
(ii) How would the flux change if the spherical Gaussian surface is replaced with a 
cubical Gaussian surface and why?  (1) 
 
7. For a given thermocouple, the emf generated across its ends is given by E = at + bt
2
 
where t in °C is the temperature of the hot junction, the cold junction being at 0 °C. If a = 
10 mV /°C and b = -0.02 mV/°C
2
, calculate the value of inversion temperature in °C.  (1) 
 
8. A 3.0 V battery is connected to an ammeter and a resistor of 3 ohms in series with it. 
What is the value of the current if the ammeter used is a galvanometer with a resistance 
of 60 ohm?  (1) 
 
9. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. 
mains. The bulb glows with some brightness. How will the glow of the bulb be affected 
on introducing a dielectric slab between the plates of the capacitor? Give reasons in 
support of your answer.  (2) 
 
10. Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two 
crossed Polaroids.  (2) 
 
11. Why is NAND gate called a universal gate. How can it to be used to realize a basic OR 
gate?  (2) 
 
12. What is modulation? What are the different types of modulation?  (2) 
 
13. Nuclear density of hydrogen is 2.3x10
17
 kg/
 
m
3
. Given A = 56 for iron, find its nuclear 
density.  (2) 
 
14. Distinguish between frequency modulation and amplitude modulation.  (2) 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
15. State Ampere’s circuital law. Write the expression for the magnetic field at the centre of 
a circular coil of radius R carrying a current I. Draw the magnetic field lines due to this 
coil.   
 (2) 
OR 
 15.0 ?F capacitor is connected to a 220V, 50Hz source. Find the capacitive reactance 
and the rms current in the circuit. If the frequency is doubled, what happens to the 
capacitive reactance and the current?  (2) 
 
16. Write the expression for the force acting on a charged particle of charge q moving with 
velocity v in the presence of a magnetic field B.  
        Show that in the presence of this force  
(i) the kinetic energy of the particle does not change.  
(ii) its instantaneous power is zero.  (2) 
 
17. In Young's double slit experiment using monochromatic light of wavelength ?, the 
intensity at a point on the screen where path difference is ?, is K units. What is the 
intensity of light at a point where path difference is ?/3?  (3) 
 
18. An electron, ?-particle and a proton have the same de-Broglie wavelength. Which of 
these particles has (i) minimum kinetic energy, (ii) maximum kinetic energy, and why?  
  (3) 
19. State the law of radioactive decay. Establish a mathematical relation between half-life 
period and disintegration constant of a radioactive nucleus.  (3) 
 
20. In the fusion reaction 1H
2
 + 1H
2 
---------> 2He
3
 + 0n
1
, the masses of deuteron, helium and 
neutron expressed in amu are 2.015, 3.017 and 1.009 respectively. If 1 kg deuterium 
undergoes complete fusion, find the amount of total energy released.  (3) 
 
21. We do not choose to transmit an audio signal by just directly converting it to an e.m. 
wave of the same frequency. Give three reasons for the same.  (3) 
 
22. A parallel plate capacitor is charged to potential V by a source of emf E. After removing 
the source, the separation between the plates is doubled.  
How will the following change: 
 
(i) electric field,  
(ii) potential difference, and  
(iii) capacitance of the capacitor? Justify your answers.  (3) 
 
 
Page 4


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
CBSE Board 
Class XII Physics 
Sample Paper - 3 
 
Time:  Three Hours Maximum Marks: 70 
 
General Instructions 
(a) All questions are compulsory. 
(b) There are 29 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 
16 carry two marks each, questions 17 to 25 carry three marks each and questions 
27 to 29 carry five marks each. 
(c) Question 26 is a value based question carrying four marks. 
(d) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each. You have to attempt only one of the given choices in such questions. 
(e) Use of calculator is not permitted. 
(f) You may use the following physical constants wherever necessary. 
-1
-1
-1
19
8
34
7
23
23
27
 C
 m s
 J s
 T ma
 J K
 /mole
 kg
1.6 10
3 10
6.6 10
4 10
1.38 10
6.023 10
1.6 10
?
?
?
?
??
??
??
??
??
??
??
o
B
A
n
e
c
h
K
N
m
?? 
 
 
1. Is the force acting between two point electric charges q 1 and q 2 kept at some distance 
apart in air, attractive or repulsive when (i) q 1q 2 > 0 (ii) q 1q 2 < 0 ?    (1) 
 
2. On a graph show the stopping potential for a given photosensitive surface varying with 
the frequencies n 1 and n 2 of incident radiations where n 1 >n 2. Given that intensity is 
same for both light radiations.   (1) 
 
3. A message signal of frequency 10 kHz is used to modulate a carrier of frequency 1 MHz. 
Find the side bands produced.  (1) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
4. Is the diode in the following circuit forward biased or reverse biased? Give reason for 
your answer.  
 (1) 
 
5. What is the frequency range of signals that are transmitted using optical fibres?  (1) 
 
6. A spherical Gaussian surface encloses charges q 1 and q 2 with                    
66
12
8.85 10 and q = - 8.85 10
??
? ? ? q C C 
(i) Calculate the electric flux passing through the surface.  
(ii) How would the flux change if the spherical Gaussian surface is replaced with a 
cubical Gaussian surface and why?  (1) 
 
7. For a given thermocouple, the emf generated across its ends is given by E = at + bt
2
 
where t in °C is the temperature of the hot junction, the cold junction being at 0 °C. If a = 
10 mV /°C and b = -0.02 mV/°C
2
, calculate the value of inversion temperature in °C.  (1) 
 
8. A 3.0 V battery is connected to an ammeter and a resistor of 3 ohms in series with it. 
What is the value of the current if the ammeter used is a galvanometer with a resistance 
of 60 ohm?  (1) 
 
9. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. 
mains. The bulb glows with some brightness. How will the glow of the bulb be affected 
on introducing a dielectric slab between the plates of the capacitor? Give reasons in 
support of your answer.  (2) 
 
10. Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two 
crossed Polaroids.  (2) 
 
11. Why is NAND gate called a universal gate. How can it to be used to realize a basic OR 
gate?  (2) 
 
12. What is modulation? What are the different types of modulation?  (2) 
 
13. Nuclear density of hydrogen is 2.3x10
17
 kg/
 
m
3
. Given A = 56 for iron, find its nuclear 
density.  (2) 
 
14. Distinguish between frequency modulation and amplitude modulation.  (2) 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
15. State Ampere’s circuital law. Write the expression for the magnetic field at the centre of 
a circular coil of radius R carrying a current I. Draw the magnetic field lines due to this 
coil.   
 (2) 
OR 
 15.0 ?F capacitor is connected to a 220V, 50Hz source. Find the capacitive reactance 
and the rms current in the circuit. If the frequency is doubled, what happens to the 
capacitive reactance and the current?  (2) 
 
16. Write the expression for the force acting on a charged particle of charge q moving with 
velocity v in the presence of a magnetic field B.  
        Show that in the presence of this force  
(i) the kinetic energy of the particle does not change.  
(ii) its instantaneous power is zero.  (2) 
 
17. In Young's double slit experiment using monochromatic light of wavelength ?, the 
intensity at a point on the screen where path difference is ?, is K units. What is the 
intensity of light at a point where path difference is ?/3?  (3) 
 
18. An electron, ?-particle and a proton have the same de-Broglie wavelength. Which of 
these particles has (i) minimum kinetic energy, (ii) maximum kinetic energy, and why?  
  (3) 
19. State the law of radioactive decay. Establish a mathematical relation between half-life 
period and disintegration constant of a radioactive nucleus.  (3) 
 
20. In the fusion reaction 1H
2
 + 1H
2 
---------> 2He
3
 + 0n
1
, the masses of deuteron, helium and 
neutron expressed in amu are 2.015, 3.017 and 1.009 respectively. If 1 kg deuterium 
undergoes complete fusion, find the amount of total energy released.  (3) 
 
21. We do not choose to transmit an audio signal by just directly converting it to an e.m. 
wave of the same frequency. Give three reasons for the same.  (3) 
 
22. A parallel plate capacitor is charged to potential V by a source of emf E. After removing 
the source, the separation between the plates is doubled.  
How will the following change: 
 
(i) electric field,  
(ii) potential difference, and  
(iii) capacitance of the capacitor? Justify your answers.  (3) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
23. For a transistor, the current amplification factor is 0.8 when the transistor is connected 
in common emitter configuration. Calculate the change in the collector current when 
the base current changes by 6 mA.  (3) 
OR 
How many electrons should be removed from a coin of mass 3.2 g, so that it just float in an 
electric field of intensity 10
10
 NC
-1
, directed upward.  (3) 
 
24. When a transistor amplifier of current gain of 75 is given an input signal, V i= 2 sin (157t 
+ ? /2), the output signal is found to be V O= 200 sin (157t +3 ? /2). 
In which mode is the transistor being used? Justify your result with proper explanation.   (3) 
 
25. The energy levels of an atom of element are shown in the following diagram. Which one 
of the level transitions will result in the emission of photons of wavelength 620 nm? 
Support your answer with mathematical calculations.  (3) 
 
   
 
26. One day Sita was coming back to home from school by her school bus. She saw a man 
was lying down at the road side and no one was there to help him. She thought it as the 
case of a major accident. She asked the driver to stop the bus and came out of the bus. 
She took the injured person to the nearest hospital taking help of a taxi.  She sent the 
patient under treatment and for the condition analysis through X-ray etc. After his first 
aid, she called her parents and explained the entire situation. Her parents felt proud of 
Sita and her bravery. When the patient became conscious she took his parents contact 
number and called them to take care of the patient. The patient's parents thanked her 
and obliged her for the help. 
 
(a) What are the values that are associated with Sita? 
(b) What is an X-ray? How it is used in the medical field?  (4) 
 
 
 
 
 
 
Page 5


  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
CBSE Board 
Class XII Physics 
Sample Paper - 3 
 
Time:  Three Hours Maximum Marks: 70 
 
General Instructions 
(a) All questions are compulsory. 
(b) There are 29 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 
16 carry two marks each, questions 17 to 25 carry three marks each and questions 
27 to 29 carry five marks each. 
(c) Question 26 is a value based question carrying four marks. 
(d) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each. You have to attempt only one of the given choices in such questions. 
(e) Use of calculator is not permitted. 
(f) You may use the following physical constants wherever necessary. 
-1
-1
-1
19
8
34
7
23
23
27
 C
 m s
 J s
 T ma
 J K
 /mole
 kg
1.6 10
3 10
6.6 10
4 10
1.38 10
6.023 10
1.6 10
?
?
?
?
??
??
??
??
??
??
??
o
B
A
n
e
c
h
K
N
m
?? 
 
 
1. Is the force acting between two point electric charges q 1 and q 2 kept at some distance 
apart in air, attractive or repulsive when (i) q 1q 2 > 0 (ii) q 1q 2 < 0 ?    (1) 
 
2. On a graph show the stopping potential for a given photosensitive surface varying with 
the frequencies n 1 and n 2 of incident radiations where n 1 >n 2. Given that intensity is 
same for both light radiations.   (1) 
 
3. A message signal of frequency 10 kHz is used to modulate a carrier of frequency 1 MHz. 
Find the side bands produced.  (1) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
4. Is the diode in the following circuit forward biased or reverse biased? Give reason for 
your answer.  
 (1) 
 
5. What is the frequency range of signals that are transmitted using optical fibres?  (1) 
 
6. A spherical Gaussian surface encloses charges q 1 and q 2 with                    
66
12
8.85 10 and q = - 8.85 10
??
? ? ? q C C 
(i) Calculate the electric flux passing through the surface.  
(ii) How would the flux change if the spherical Gaussian surface is replaced with a 
cubical Gaussian surface and why?  (1) 
 
7. For a given thermocouple, the emf generated across its ends is given by E = at + bt
2
 
where t in °C is the temperature of the hot junction, the cold junction being at 0 °C. If a = 
10 mV /°C and b = -0.02 mV/°C
2
, calculate the value of inversion temperature in °C.  (1) 
 
8. A 3.0 V battery is connected to an ammeter and a resistor of 3 ohms in series with it. 
What is the value of the current if the ammeter used is a galvanometer with a resistance 
of 60 ohm?  (1) 
 
9. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. 
mains. The bulb glows with some brightness. How will the glow of the bulb be affected 
on introducing a dielectric slab between the plates of the capacitor? Give reasons in 
support of your answer.  (2) 
 
10. Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two 
crossed Polaroids.  (2) 
 
11. Why is NAND gate called a universal gate. How can it to be used to realize a basic OR 
gate?  (2) 
 
12. What is modulation? What are the different types of modulation?  (2) 
 
13. Nuclear density of hydrogen is 2.3x10
17
 kg/
 
m
3
. Given A = 56 for iron, find its nuclear 
density.  (2) 
 
14. Distinguish between frequency modulation and amplitude modulation.  (2) 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
15. State Ampere’s circuital law. Write the expression for the magnetic field at the centre of 
a circular coil of radius R carrying a current I. Draw the magnetic field lines due to this 
coil.   
 (2) 
OR 
 15.0 ?F capacitor is connected to a 220V, 50Hz source. Find the capacitive reactance 
and the rms current in the circuit. If the frequency is doubled, what happens to the 
capacitive reactance and the current?  (2) 
 
16. Write the expression for the force acting on a charged particle of charge q moving with 
velocity v in the presence of a magnetic field B.  
        Show that in the presence of this force  
(i) the kinetic energy of the particle does not change.  
(ii) its instantaneous power is zero.  (2) 
 
17. In Young's double slit experiment using monochromatic light of wavelength ?, the 
intensity at a point on the screen where path difference is ?, is K units. What is the 
intensity of light at a point where path difference is ?/3?  (3) 
 
18. An electron, ?-particle and a proton have the same de-Broglie wavelength. Which of 
these particles has (i) minimum kinetic energy, (ii) maximum kinetic energy, and why?  
  (3) 
19. State the law of radioactive decay. Establish a mathematical relation between half-life 
period and disintegration constant of a radioactive nucleus.  (3) 
 
20. In the fusion reaction 1H
2
 + 1H
2 
---------> 2He
3
 + 0n
1
, the masses of deuteron, helium and 
neutron expressed in amu are 2.015, 3.017 and 1.009 respectively. If 1 kg deuterium 
undergoes complete fusion, find the amount of total energy released.  (3) 
 
21. We do not choose to transmit an audio signal by just directly converting it to an e.m. 
wave of the same frequency. Give three reasons for the same.  (3) 
 
22. A parallel plate capacitor is charged to potential V by a source of emf E. After removing 
the source, the separation between the plates is doubled.  
How will the following change: 
 
(i) electric field,  
(ii) potential difference, and  
(iii) capacitance of the capacitor? Justify your answers.  (3) 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
23. For a transistor, the current amplification factor is 0.8 when the transistor is connected 
in common emitter configuration. Calculate the change in the collector current when 
the base current changes by 6 mA.  (3) 
OR 
How many electrons should be removed from a coin of mass 3.2 g, so that it just float in an 
electric field of intensity 10
10
 NC
-1
, directed upward.  (3) 
 
24. When a transistor amplifier of current gain of 75 is given an input signal, V i= 2 sin (157t 
+ ? /2), the output signal is found to be V O= 200 sin (157t +3 ? /2). 
In which mode is the transistor being used? Justify your result with proper explanation.   (3) 
 
25. The energy levels of an atom of element are shown in the following diagram. Which one 
of the level transitions will result in the emission of photons of wavelength 620 nm? 
Support your answer with mathematical calculations.  (3) 
 
   
 
26. One day Sita was coming back to home from school by her school bus. She saw a man 
was lying down at the road side and no one was there to help him. She thought it as the 
case of a major accident. She asked the driver to stop the bus and came out of the bus. 
She took the injured person to the nearest hospital taking help of a taxi.  She sent the 
patient under treatment and for the condition analysis through X-ray etc. After his first 
aid, she called her parents and explained the entire situation. Her parents felt proud of 
Sita and her bravery. When the patient became conscious she took his parents contact 
number and called them to take care of the patient. The patient's parents thanked her 
and obliged her for the help. 
 
(a) What are the values that are associated with Sita? 
(b) What is an X-ray? How it is used in the medical field?  (4) 
 
 
 
 
 
 
  
 
CBSE XII  |  PHYSICS 
Sample Paper – 3 
 
     
 
27.  
(a) Define the term dipole moment and its direction. State its SI unit. Deduce the 
expression for the torque acting on it.  
(b) In a particular situation, it has its dipole moment aligned with the electric field. Is 
the equilibrium stable or unstable?  (5 marks) 
OR 
A transistor is used in common emitter mode in an amplifier circuit. When a signal of 
20 mV is added to the base-emitter voltage, the base current changes by 20 A ? and 
the collector current changes by 2 mA. The load resistance is 5k ? . Calculate (a) the 
factor ? , (b) the input resistance R BE, (c) the transconductance and (d) the voltage 
gain.  (5) 
 
28.  
(a) State Lenz’s law. Which conservation law can be used to explain this law? 
(b) A wheel with 10 metallic spokes each 0.5m long is rotated with a speed of 
120rev/min in a plane normal to the horizontal component of earth’s magnetic field 
at a place where the earth’s field is 0.4x10
-4
G. What is the induced emf between the 
axle and the rim of the wheel?  
(c) Two moving coil meters, M 1 and M 2 have the following particulars: 
R 1 = 10  , N 1 = 30, 
A 1 = 3.6 x 10
-3
 m
2
, B 1 = 0.25 T 
R 2 = 14  , N 2 = 42 
A 2 = 1.8 x 10
-3
 m
2
, B 2 = 0.50 T 
(The spring constants are identical for the two meters). Determine the ratio of (a) 
current sensitivity and (b) voltage sensitivity of M 2 and M 1.    (5) 
OR 
(a) An electron & a proton moving with the same speed enter a uniform magnetic field 
B perpendicularly. Which particle will have larger radius of its circular path? Find 
the ratio of their radii. The masses of electron & proton are 9.1 x 10
-31
 kg & 1.67 x 
10
-27
 kg.  
(b) Show that for a moving charged particle in a uniform magnetic field, the kinetic 
energy of the particle remains constant. 
(c) A coil placed in the plane of the page has a current in the clockwise direction when 
looking from above. What will be the change in the magnetic field at the center of 
the coil if  
(i) the current through the coil is reduced to half? 
(ii) radius of the coil is doubled ? 
(iii) what will be the direction of the magnetic field?   (5 marks)