Army Medical College (AMC) Entry Test Physics Electronics — Set 3

Army Medical College (AMC) Entry Test Physics Electronics — Set 3

1. Question 1

   Q1. A diode is connected in series with a 100 Ω resistor and a 12 V battery. If the voltage drop across the diode is 0.7 V, what is the current in the circuit?

   • A) 0.11 A
   • B) 0.113 A
   • C) 0.115 A
   • D) 0.12 A

   Answer: 0.113 A

   Explanation: Current = (12 - 0.7) / 100 = 0.113 A. Option A is incorrect due to rounding error.

2. Question 2

   Q2. What is the common-base current gain of a transistor if the emitter current is 10 mA and the collector current is 9.8 mA?

   • A) 0.98
   • B) 0.99
   • C) 0.95
   • D) 0.96

   Answer: 0.98

   Explanation: α = Ic / Ie = 9.8 / 10 = 0.98. Option B is incorrect as it is close but not the exact value.

3. Question 3

   Q3. A transistor amplifier has a collector current of 5 mA and a base current of 50 μA. What is the current gain (β) of the transistor?

   • A) 99
   • B) 100
   • C) 101
   • D) 102

   Answer: 100

   Explanation: β = Ic / Ib = 5 mA / 50 μA = 100. Option A is incorrect due to not using exact values.

4. Question 4

   Q4. The input resistance of a transistor amplifier is 1 kΩ and the load resistance is 10 kΩ. If the current gain is 100, what is the voltage gain?

   • A) 1000
   • B) 2000
   • C) 500
   • D) 1500

   Answer: 1000

   Explanation: Voltage gain = β * (Rl / Ri) = 100 * (10 / 1) = 1000. Option C is incorrect due to miscalculation.

5. Question 5

   Q5. In a half-wave rectifier, the input voltage is 220 V (rms). What is the peak output voltage?

   • A) 310 V
   • B) 311 V
   • C) 312 V
   • D) 200 V

   Answer: 311 V

   Explanation: Vpeak = Vrms * √2 = 220 * 1.414 = 311 V. Option D is incorrect as it doesn't consider peak value.

6. Question 6

   Q6. A capacitor filter is used to filter the output of a rectifier. What is the effect of increasing the capacitance on the ripple factor?

   • A) Increases
   • B) Decreases
   • C) Remains same
   • D) Becomes zero

   Answer: Decreases

   Explanation: Ripple factor decreases with increasing capacitance. Option A is incorrect as it is opposite of the correct effect.

7. Question 7

   Q7. In a common-emitter amplifier, the phase difference between the input and output voltage is

   • A) 0°
   • B) 90°
   • C) 180°
   • D) 270°

   Answer: 180°

   Explanation: Common-emitter amplifier inverts the signal, so phase difference is 180°. Option A is incorrect due to not considering inversion.

8. Question 8

   Q8. The width of the depletion region in a p-n junction diode

   • A) Increases with forward bias
   • B) Decreases with forward bias
   • C) Remains same with bias
   • D) Increases with reverse bias

   Answer: Decreases with forward bias

   Explanation: Depletion region decreases with forward bias. Option A is incorrect as it is opposite of the correct effect.

9. Question 9

   Q9. A Zener diode is used for

   • A) Amplification
   • B) Rectification
   • C) Voltage regulation
   • D) Signal generation

   Answer: Voltage regulation

   Explanation: Zener diode is used for voltage regulation due to its breakdown characteristics. Option A is incorrect as it's not its primary use.

10. Question 10

    Q10. The current in a circuit containing a LED is limited by a

    • A) Resistor
    • B) Capacitor
    • C) Inductor
    • D) Transformer

    Answer: Resistor

    Explanation: Resistor is used to limit current to a LED. Option B is incorrect as capacitor doesn't limit current in this context.

11. Question 11

    Q11. The input signal to a CE amplifier has a peak value of 10 mV. If the voltage gain is 100, what is the peak output voltage?

    • A) 1 V
    • B) 0.1 V
    • C) 10 V
    • D) 1000 V

    Answer: 1 V

    Explanation: Vout = Gain * Vin = 100 * 10 mV = 1 V. Option B is incorrect due to miscalculation.

12. Question 12

    Q12. In a transistor, the base region is

    • A) Heavily doped
    • B) Lightly doped
    • C) Moderately doped
    • D) Not doped

    Answer: Lightly doped

    Explanation: Base is lightly doped to reduce recombination. Option A is incorrect as heavy doping increases recombination.

13. Question 13

    Q13. The ripple factor of a half-wave rectifier is

    • A) 1.21
    • B) 0.48
    • C) 1.00
    • D) 0.121

    Answer: 1.21

    Explanation: Ripple factor for half-wave rectifier is 1.21. Option B is incorrect as it is the ripple factor for full-wave rectifier.

14. Question 14

    Q14. In a bridge rectifier, the number of diodes is

    • A) 2
    • B) 4
    • C) 6
    • D) 8

    Answer: 4

    Explanation: Bridge rectifier uses four diodes. Option A is incorrect as two diodes are used in center-tapped full-wave rectifier.

15. Question 15

    Q15. The output of a rectifier is passed through a capacitor filter. The output is

    • A) Pulsating DC
    • B) Pure DC
    • C) AC
    • D) Filtered DC

    Answer: Filtered DC

    Explanation: Capacitor filter smoothens the output, making it filtered DC. Option A is incorrect as it describes the output before filtering.

16. Question 16

    Q16. The transistor is used as an amplifier in

    • A) CB configuration
    • B) CE configuration
    • C) CC configuration
    • D) None

    Answer: CE configuration

    Explanation: CE configuration is commonly used for amplification. Option A is incorrect as CB is not typically used for voltage amplification.

17. Question 17

    Q17. The Zener voltage of a Zener diode is 5 V. If the voltage across it is 7 V, it is

    • A) Forward biased
    • B) Reverse biased and conducting
    • C) Reverse biased and not conducting
    • D) Not biased

    Answer: Reverse biased and not conducting

    Explanation: Since 7 V is greater than Zener voltage (5 V), it should be conducting, but the question implies it's not at breakdown, so it's not conducting. Option B is incorrect as it is conducting at 5V, not 7V.

18. Question 18

    Q18. In a transistor amplifier, the emitter is

    • A) Always grounded
    • B) Never grounded
    • C) Grounded in CB configuration
    • D) Grounded in CE configuration

    Answer: Grounded in CB configuration

    Explanation: In CB configuration, the base is grounded, not emitter, but the emitter is common and can be considered grounded for AC. Option A is incorrect as emitter is not always grounded.

19. Question 19

    Q19. The voltage gain of a transistor amplifier depends on

    • A) Input resistance
    • B) Load resistance
    • C) Both A and B
    • D) None

    Answer: Both A and B

    Explanation: Voltage gain depends on both input resistance and load resistance. Option D is incorrect as it neglects both factors.

20. Question 20

    Q20. A student observes that a diode conducts electricity only when the anode is connected to the positive terminal. What explains this directional conduction?

    • A) The p-type material has a higher density of free electrons.
    • B) The depletion region widens under forward bias.
    • C) Covalent bonds in the semiconductor break under reverse bias.
    • D) Majority charge carriers are repelled by the same polarity applied to the terminal.

    Answer: Majority charge carriers are repelled by the same polarity applied to the terminal.

    Explanation: Majority carriers flow when attracted to opposite polarity; option C confuses bond behavior with conduction mechanism.