Semiconductor JEE Main - Physics, Solution by DC Pandey | DC Pandey Solutions for JEE Physics

 Page 1


Exercises 
Objective Questions 
  Single Correct Option 
Q 1.  The conductivity of a semiconductor increases with increase in temperature because 
  (a) number density of free current carriers increases 
  (b) relaxation time increases 
(c) both number density of carriers and relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density. 
(d) number density of current carriers increases, relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density 
Q 2.  In figure, assuming the diodes to be ideal, 
 
  (a) D
1
 is forward biased and D
2
 is reverse biased and hence current flows from A to B. 
(b) D
2
 is forward biased and D
1
 is reverse biased and hence no current flows from B to A and vice-
versa. 
  (c) D
1
 and D
2
 are both forward biased and hence current flows from A to B. 
  (d) D
1
 and D
2
 are both reverse biased and hence no current flows from A to B and vice-versa. 
Q 3.  Hole is 
  (a) an anti-particle of electron   
  (b) a vacancy created when an electron leaves a covalent bond 
  (c) absence of free electrons 
  (d) an artificially created particle 
Q 4.  A 220 V AC. supply is connected between points A and B. What will be the potential difference V 
across the capacitor? 
 
  (a) 220V   (b) 110V  (c) 0 V   (d) 220 2 V 
  More than One Correct Options 
Q 5.  When an electric field is applied across a semiconductor, 
  (a) electrons move from lower energy level to higher energy level in the conduction band. 
  (b) electrons move from higher energy level to lower energy level in the conduction band. 
  (c) holes in the valence band move from higher energy level to lower energy level. 
Page 2


Exercises 
Objective Questions 
  Single Correct Option 
Q 1.  The conductivity of a semiconductor increases with increase in temperature because 
  (a) number density of free current carriers increases 
  (b) relaxation time increases 
(c) both number density of carriers and relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density. 
(d) number density of current carriers increases, relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density 
Q 2.  In figure, assuming the diodes to be ideal, 
 
  (a) D
1
 is forward biased and D
2
 is reverse biased and hence current flows from A to B. 
(b) D
2
 is forward biased and D
1
 is reverse biased and hence no current flows from B to A and vice-
versa. 
  (c) D
1
 and D
2
 are both forward biased and hence current flows from A to B. 
  (d) D
1
 and D
2
 are both reverse biased and hence no current flows from A to B and vice-versa. 
Q 3.  Hole is 
  (a) an anti-particle of electron   
  (b) a vacancy created when an electron leaves a covalent bond 
  (c) absence of free electrons 
  (d) an artificially created particle 
Q 4.  A 220 V AC. supply is connected between points A and B. What will be the potential difference V 
across the capacitor? 
 
  (a) 220V   (b) 110V  (c) 0 V   (d) 220 2 V 
  More than One Correct Options 
Q 5.  When an electric field is applied across a semiconductor, 
  (a) electrons move from lower energy level to higher energy level in the conduction band. 
  (b) electrons move from higher energy level to lower energy level in the conduction band. 
  (c) holes in the valence band move from higher energy level to lower energy level. 
  (d) holes in the valence band move from lower energy level to higher energy level. 
Q 6.  Consider an n-p-n transistor with its base-emitter junction forward biased and collector base 
junction reverse biased. Which of the following statements are true? 
  (a) Electrons crossover from emitter to collector. (b) Holes move from base to collector. 
  (c) Electrons move from emitter to base. 
  (d) Electrons from emitter move out of base without going to the collector. 
Q 7.  In a n-p-n transistor circuit, the collector current is 10 mA. If 95 per cent of the electrons emitted 
reach the collector, which of the following statements are true? 
  (a) The emitter current will be 8 mA.  (b) The emitter current will be 10.53 mA. 
  (c) The base current will be 0.53 mA. (d) The base current will be 2 mA. 
Q 8.  In the depletion region of a diode 
  (a) there are no mobile charges   
  (b) equal number of holes and electrons exist, making the region neutral 
  (c) recombination of holes and electrons has taken place 
  (d) immobile charged ions exist. 
Q 9.  What happens during regulation action of a Zener diode? 
  (a) The current and voltage across the Zener remains fixed. 
  (b) The current through the series Resistance (R) changes.  
  (c) The Zener resistance is constant. 
  (d) The resistance offered by the Zener changes. 
Q 10.  The breakdown in a reverse biased p-n junction diode is more likely to occur due to 
  (a) large velocity of the minority charge carriers if the doping concentration is small 
  (b) large velocity of the minority charge carriers if the doping concentration is large 
  (c) strong electric field in a depletion region if the doping concentration is small 
  (d) strong electric field in the depletion region if the doping concentration is large. 
Subjective Questions 
Q 11.  Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter 
across the junction? 
Q 12.  Two car garages have a common gate which needs to open automatically when a car enters either 
of the garages or cars enter both. Devise a circuit that resembles this situation using diodes for this 
situation. 
Q 13.  Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a 
voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 V, calculate 
the output AC signal. 
Q 14.  A p-n photodiode is fabricated from a semiconductor with band-gap of 2.8 eV. Can it detect a 
wavelength of 6000 nm? 
Page 3


Exercises 
Objective Questions 
  Single Correct Option 
Q 1.  The conductivity of a semiconductor increases with increase in temperature because 
  (a) number density of free current carriers increases 
  (b) relaxation time increases 
(c) both number density of carriers and relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density. 
(d) number density of current carriers increases, relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density 
Q 2.  In figure, assuming the diodes to be ideal, 
 
  (a) D
1
 is forward biased and D
2
 is reverse biased and hence current flows from A to B. 
(b) D
2
 is forward biased and D
1
 is reverse biased and hence no current flows from B to A and vice-
versa. 
  (c) D
1
 and D
2
 are both forward biased and hence current flows from A to B. 
  (d) D
1
 and D
2
 are both reverse biased and hence no current flows from A to B and vice-versa. 
Q 3.  Hole is 
  (a) an anti-particle of electron   
  (b) a vacancy created when an electron leaves a covalent bond 
  (c) absence of free electrons 
  (d) an artificially created particle 
Q 4.  A 220 V AC. supply is connected between points A and B. What will be the potential difference V 
across the capacitor? 
 
  (a) 220V   (b) 110V  (c) 0 V   (d) 220 2 V 
  More than One Correct Options 
Q 5.  When an electric field is applied across a semiconductor, 
  (a) electrons move from lower energy level to higher energy level in the conduction band. 
  (b) electrons move from higher energy level to lower energy level in the conduction band. 
  (c) holes in the valence band move from higher energy level to lower energy level. 
  (d) holes in the valence band move from lower energy level to higher energy level. 
Q 6.  Consider an n-p-n transistor with its base-emitter junction forward biased and collector base 
junction reverse biased. Which of the following statements are true? 
  (a) Electrons crossover from emitter to collector. (b) Holes move from base to collector. 
  (c) Electrons move from emitter to base. 
  (d) Electrons from emitter move out of base without going to the collector. 
Q 7.  In a n-p-n transistor circuit, the collector current is 10 mA. If 95 per cent of the electrons emitted 
reach the collector, which of the following statements are true? 
  (a) The emitter current will be 8 mA.  (b) The emitter current will be 10.53 mA. 
  (c) The base current will be 0.53 mA. (d) The base current will be 2 mA. 
Q 8.  In the depletion region of a diode 
  (a) there are no mobile charges   
  (b) equal number of holes and electrons exist, making the region neutral 
  (c) recombination of holes and electrons has taken place 
  (d) immobile charged ions exist. 
Q 9.  What happens during regulation action of a Zener diode? 
  (a) The current and voltage across the Zener remains fixed. 
  (b) The current through the series Resistance (R) changes.  
  (c) The Zener resistance is constant. 
  (d) The resistance offered by the Zener changes. 
Q 10.  The breakdown in a reverse biased p-n junction diode is more likely to occur due to 
  (a) large velocity of the minority charge carriers if the doping concentration is small 
  (b) large velocity of the minority charge carriers if the doping concentration is large 
  (c) strong electric field in a depletion region if the doping concentration is small 
  (d) strong electric field in the depletion region if the doping concentration is large. 
Subjective Questions 
Q 11.  Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter 
across the junction? 
Q 12.  Two car garages have a common gate which needs to open automatically when a car enters either 
of the garages or cars enter both. Devise a circuit that resembles this situation using diodes for this 
situation. 
Q 13.  Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a 
voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 V, calculate 
the output AC signal. 
Q 14.  A p-n photodiode is fabricated from a semiconductor with band-gap of 2.8 eV. Can it detect a 
wavelength of 6000 nm? 
Q 15.  The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 
and 30, respectively and the input signal is 1 mV peak value, then what is the output signal voltage 
(peak value) (i) if DC supply voltage is 10V? (ii) if DC supply voltage is 5 V? 
Q 16.  (i) Name the type of a diode whose characteristics are shown in figure, (ii) What does the point P 
in figure represent? 
 
Q 17.  If the resistance R
1
 is increased, how will the readings of the ammeter and voltmeter change? 
 
Q 18.  How would you set up a circuit to obtain NOT gate using a transistor? 
Q 19.  Write the truth table for the circuit shown in figure. Name the gate that the circuit resembles. 
 
Q 20.  A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5V 
and it has to regulate voltage which fluctuated between 3V and 7V, what should be the value of R 
for safe operation.  
 
Q 21.  If each diode in figure has a forward bias resistance of 25 ? and infinite resistance in reverse bias, 
what will be the values of the current I
1
, I
2
, I
3 
and I
4
? 
Page 4


Exercises 
Objective Questions 
  Single Correct Option 
Q 1.  The conductivity of a semiconductor increases with increase in temperature because 
  (a) number density of free current carriers increases 
  (b) relaxation time increases 
(c) both number density of carriers and relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density. 
(d) number density of current carriers increases, relaxation time decreases but effect of decrease in 
relaxation time is much less than increase in number density 
Q 2.  In figure, assuming the diodes to be ideal, 
 
  (a) D
1
 is forward biased and D
2
 is reverse biased and hence current flows from A to B. 
(b) D
2
 is forward biased and D
1
 is reverse biased and hence no current flows from B to A and vice-
versa. 
  (c) D
1
 and D
2
 are both forward biased and hence current flows from A to B. 
  (d) D
1
 and D
2
 are both reverse biased and hence no current flows from A to B and vice-versa. 
Q 3.  Hole is 
  (a) an anti-particle of electron   
  (b) a vacancy created when an electron leaves a covalent bond 
  (c) absence of free electrons 
  (d) an artificially created particle 
Q 4.  A 220 V AC. supply is connected between points A and B. What will be the potential difference V 
across the capacitor? 
 
  (a) 220V   (b) 110V  (c) 0 V   (d) 220 2 V 
  More than One Correct Options 
Q 5.  When an electric field is applied across a semiconductor, 
  (a) electrons move from lower energy level to higher energy level in the conduction band. 
  (b) electrons move from higher energy level to lower energy level in the conduction band. 
  (c) holes in the valence band move from higher energy level to lower energy level. 
  (d) holes in the valence band move from lower energy level to higher energy level. 
Q 6.  Consider an n-p-n transistor with its base-emitter junction forward biased and collector base 
junction reverse biased. Which of the following statements are true? 
  (a) Electrons crossover from emitter to collector. (b) Holes move from base to collector. 
  (c) Electrons move from emitter to base. 
  (d) Electrons from emitter move out of base without going to the collector. 
Q 7.  In a n-p-n transistor circuit, the collector current is 10 mA. If 95 per cent of the electrons emitted 
reach the collector, which of the following statements are true? 
  (a) The emitter current will be 8 mA.  (b) The emitter current will be 10.53 mA. 
  (c) The base current will be 0.53 mA. (d) The base current will be 2 mA. 
Q 8.  In the depletion region of a diode 
  (a) there are no mobile charges   
  (b) equal number of holes and electrons exist, making the region neutral 
  (c) recombination of holes and electrons has taken place 
  (d) immobile charged ions exist. 
Q 9.  What happens during regulation action of a Zener diode? 
  (a) The current and voltage across the Zener remains fixed. 
  (b) The current through the series Resistance (R) changes.  
  (c) The Zener resistance is constant. 
  (d) The resistance offered by the Zener changes. 
Q 10.  The breakdown in a reverse biased p-n junction diode is more likely to occur due to 
  (a) large velocity of the minority charge carriers if the doping concentration is small 
  (b) large velocity of the minority charge carriers if the doping concentration is large 
  (c) strong electric field in a depletion region if the doping concentration is small 
  (d) strong electric field in the depletion region if the doping concentration is large. 
Subjective Questions 
Q 11.  Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter 
across the junction? 
Q 12.  Two car garages have a common gate which needs to open automatically when a car enters either 
of the garages or cars enter both. Devise a circuit that resembles this situation using diodes for this 
situation. 
Q 13.  Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a 
voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 V, calculate 
the output AC signal. 
Q 14.  A p-n photodiode is fabricated from a semiconductor with band-gap of 2.8 eV. Can it detect a 
wavelength of 6000 nm? 
Q 15.  The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 
and 30, respectively and the input signal is 1 mV peak value, then what is the output signal voltage 
(peak value) (i) if DC supply voltage is 10V? (ii) if DC supply voltage is 5 V? 
Q 16.  (i) Name the type of a diode whose characteristics are shown in figure, (ii) What does the point P 
in figure represent? 
 
Q 17.  If the resistance R
1
 is increased, how will the readings of the ammeter and voltmeter change? 
 
Q 18.  How would you set up a circuit to obtain NOT gate using a transistor? 
Q 19.  Write the truth table for the circuit shown in figure. Name the gate that the circuit resembles. 
 
Q 20.  A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5V 
and it has to regulate voltage which fluctuated between 3V and 7V, what should be the value of R 
for safe operation.  
 
Q 21.  If each diode in figure has a forward bias resistance of 25 ? and infinite resistance in reverse bias, 
what will be the values of the current I
1
, I
2
, I
3 
and I
4
? 
 
Q 22.  In the circuit shown in figure when the input voltage of the base resistance is 10V, V
be
 is zero and 
V
ce
 is also zero. Find the values of I
b
, I
c
 and ?. 
 
Q 23.  For the transistor circuit shown in figure, evaluate V
E
, R
B
 and R
E
 .Given I
C
 = 1 mA, V
CE
 = 3V,V
BE
 
= 0.5 V, V
CC
 = 12V and ? = 100 
Q 24.  In the circuit shown in figure, find the value of R
C
.  
 
 
 
Exercises 
  1. (d) 2. (b) 3. (b) 4. (d) 5. (a,c) 6. (a,c) 7. (b,c) 8. (a,b,d) 9. (b,d) 10. (a,d) 
11. No   12. OR gate  13. 2V   14. No   15. (i) 6V (ii) 5 V 
16. (i) Zener junction diode and solar cell (ii) Zener breakdown voltage 
17. Both readings will decrease  18. See the hints  19. AND gate   20.10 ? 
21. I
1
 = 0.05A, I
2
 = 0.025A, I
3
 = 0, I
4
 = 0.025A 
22. I
b
 = 25 ?A, I
c
 = 3.33 mA, ?
 
=133   
23. V
E
 = 1.2 V,R
B
 = 108 k?, R
E
 = 1. 2k ?  
24. 0.56 k?