UHS Punjab MDCAT Physics: Electronics MCQs

UHS Punjab MDCAT Physics: Electronics MCQs — sample questions

1. Question 1

   Q1. In an NPN transistor, the majority charge carriers in the base region are

   • A) electrons
   • B) holes
   • C) protons
   • D) neutrons

   Answer: holes

   Explanation: Holes are majority carriers in the P-type base region. Electrons are majority carriers in N-type regions.

2. Question 2

   Q2. The input resistance of an ideal operational amplifier is

   • A) zero
   • B) very low
   • C) very high
   • D) infinite

   Answer: infinite

   Explanation: Ideal op-amp has infinite input resistance. Real op-amps have very high input resistance.

3. Question 3

   Q3. A Zener diode is used as a

   • A) rectifier
   • B) voltage regulator
   • C) amplifier
   • D) oscillator

   Answer: voltage regulator

   Explanation: Zener diodes regulate voltage due to their specific reverse breakdown voltage.

4. Question 4

   Q4. The gain of a common emitter amplifier is given by

   • A) R_E/R_B
   • B) R_C/R_E
   • C) R_C/R_B
   • D) β*R_C/R_B

   Answer: β*R_C/R_B

   Explanation: Common emitter gain is β times the ratio of collector resistance to base resistance.

5. Question 5

   Q5. The width of the depletion region in a PN junction diode increases when

   • A) forward biased
   • B) reverse biased
   • C) at zero bias
   • D) at high temperature

   Answer: reverse biased

   Explanation: Reverse bias increases depletion width. Forward bias decreases it.

6. Question 6

   Q6. A logic gate that produces an output only when all inputs are different is called

   • A) AND gate
   • B) OR gate
   • C) XOR gate
   • D) NOT gate

   Answer: XOR gate

   Explanation: XOR gate outputs 1 when inputs are different. AND and OR gates have different conditions.

7. Question 7

   Q7. The current gain of a transistor in common base configuration is

   • A) less than 1
   • B) equal to 1
   • C) greater than 1
   • D) very large

   Answer: less than 1

   Explanation: Common base current gain is α, which is less than 1. It's typically around 0.98.

8. Question 8

   Q8. The output of a rectifier circuit is

   • A) AC
   • B) DC
   • C) pulsating DC
   • D) mixed AC and DC

   Answer: pulsating DC

   Explanation: Rectifiers convert AC to pulsating DC. Further filtering is needed for pure DC.

9. Question 9

   Q9. The Boolean expression for the output of a NAND gate is

   • A) A*B
   • B) A+B
   • C) A'*B'
   • D) (A*B)'

   Answer: (A*B)'

   Explanation: NAND gate output is the negation of AND operation, hence (A*B)'.

10. Question 10

    Q10. In a half-wave rectifier, the frequency of the output is

    • A) same as input frequency
    • B) twice the input frequency
    • C) half the input frequency
    • D) four times the input frequency

    Answer: same as input frequency

    Explanation: Half-wave rectification maintains the same frequency as the input AC.

11. Question 11

    Q11. A transistor amplifier is said to be in class A operation when

    • A) the collector current flows for the entire cycle
    • B) the collector current flows for half the cycle
    • C) the collector current flows for more than half but less than the entire cycle
    • D) the collector current is zero

    Answer: the collector current flows for the entire cycle

    Explanation: Class A amplifiers have collector current throughout the input cycle.

12. Question 12

    Q12. The forbidden energy gap in a semiconductor is

    • A) the energy required to break a covalent bond
    • B) the energy required to move an electron from valence to conduction band
    • C) the energy released when an electron falls from conduction to valence band
    • D) the energy required to remove an electron from a metal surface

    Answer: the energy required to move an electron from valence to conduction band

    Explanation: Forbidden energy gap is the energy difference between valence and conduction bands.

13. Question 13

    Q13. The device used to store electric charge is called

    • A) capacitor
    • B) inductor
    • C) resistor
    • D) transformer

    Answer: capacitor

    Explanation: Capacitors store electric charge. Inductors store magnetic energy.

14. Question 14

    Q14. The common mode rejection ratio (CMRR) is a measure of

    • A) the ability of an op-amp to reject common mode signals
    • B) the gain of an op-amp
    • C) the input resistance of an op-amp
    • D) the output resistance of an op-amp

    Answer: the ability of an op-amp to reject common mode signals

    Explanation: CMRR measures an op-amp's ability to reject signals common to both inputs.

15. Question 15

    Q15. The potential barrier across a PN junction is

    • A) 0.3 V for Ge and 0.7 V for Si
    • B) 0.7 V for Ge and 0.3 V for Si
    • C) same for Ge and Si
    • D) zero for both Ge and Si

    Answer: 0.3 V for Ge and 0.7 V for Si

    Explanation: Potential barrier is 0.3 V for Ge and 0.7 V for Si due to different material properties.

16. Question 16

    Q16. The emitter of a transistor is

    • A) heavily doped
    • B) lightly doped
    • C) moderately doped
    • D) undoped

    Answer: heavily doped

    Explanation: Emitter is heavily doped to supply majority carriers. Base is lightly doped.

17. Question 17

    Q17. The output of an operational amplifier is

    • A) proportional to the difference between the two input voltages
    • B) proportional to the sum of the two input voltages
    • C) proportional to the product of the two input voltages
    • D) independent of the input voltages

    Answer: proportional to the difference between the two input voltages

    Explanation: Op-amp output is proportional to the differential input voltage, not sum or product.

18. Question 18

    Q18. A clamper circuit is used to

    • A) change the DC level of a waveform
    • B) change the amplitude of a waveform
    • C) filter out unwanted frequencies
    • D) amplify a signal

    Answer: change the DC level of a waveform

    Explanation: Clampers shift the DC level of a waveform without changing its shape.

19. Question 19

    Q19. The typical application of a tunnel diode is in

    • A) oscillators
    • B) amplifiers
    • C) rectifiers
    • D) switches

    Answer: oscillators

    Explanation: Tunnel diodes are used in oscillators due to their negative resistance region.

20. Question 20

    Q20. The efficiency of a half-wave rectifier is approximately

    • A) 40.6%
    • B) 50%
    • C) 81.2%
    • D) 100%

    Answer: 40.6%

    Explanation: Half-wave rectifier efficiency is about 40.6%. Full-wave is more efficient.