Bahria University Entry Test Physics Electronics — Set 2

Electronics MCQs set 2 for Bahria University Entry Test Physics — 20 solved questions.

Bahria University Entry Test Physics Electronics — Set 2

  1. Question 1

    Q1. In a p-n junction, the depletion layer is due to

    • A) majority carriers
    • B) minority carriers
    • C) immobile ions
    • D) both majority and minority carriers

    Answer: immobile ions

    Explanation: Depletion layer is formed due to immobile ions left behind after majority carriers diffuse across the junction.

  2. Question 2

    Q2. The voltage gain of an amplifier with negative feedback is

    • A) inversely proportional to feedback fraction
    • B) directly proportional to feedback fraction
    • C) independent of feedback fraction
    • D) proportional to square of feedback fraction

    Answer: inversely proportional to feedback fraction

    Explanation: Voltage gain with feedback = A / (1 + βA), for large A, gain is inversely proportional to β.

  3. Question 3

    Q3. A diode having a forward resistance of 50 Ω is used for half-wave rectification. The input voltage is 220 V (rms). The load resistance is 1 kΩ. The output dc current is

    • A) 0.198 A
    • B) 0.099 A
    • C) 0.297 A
    • D) 0.396 A

    Answer: 0.099 A

    Explanation: Idc = Im / π = Vm / (π * (Rf + Rl)) = 220√2 / (π * (50 + 1000)) = 0.099 A.

  4. Question 4

    Q4. The bandwidth of an amplifier is

    • A) inversely proportional to gain
    • B) directly proportional to gain
    • C) independent of gain
    • D) proportional to square of gain

    Answer: inversely proportional to gain

    Explanation: Bandwidth = f2 - f1, gain-bandwidth product is constant, hence bandwidth is inversely proportional to gain.

  5. Question 5

    Q5. A transistor is operated in common emitter configuration. The collector supply voltage is 10 V and the voltage drop across a resistor of 1 kΩ in the collector circuit is 0.7 V. The collector current is

    • A) 0.7 mA
    • B) 7 mA
    • C) 0.07 mA
    • D) 70 mA

    Answer: 0.7 mA

    Explanation: Ic = Vc / Rc = 0.7 V / 1 kΩ = 0.7 mA.

  6. Question 6

    Q6. In a CE amplifier, the output voltage is

    • A) in phase with input voltage
    • B) out of phase with input voltage by 90°
    • C) out of phase with input voltage by 180°
    • D) out of phase with input voltage by 270°

    Answer: out of phase with input voltage by 180°

    Explanation: CE amplifier inverts the input signal, hence output is 180° out of phase.

  7. Question 7

    Q7. The emitter current in a transistor is

    • A) equal to the sum of base and collector currents
    • B) equal to the difference of base and collector currents
    • C) twice the collector current
    • D) half the collector current

    Answer: equal to the sum of base and collector currents

    Explanation: Ie = Ib + Ic, emitter current is the sum of base and collector currents.

  8. Question 8

    Q8. A Zener diode is used for

    • A) amplification
    • B) rectification
    • C) stabilization
    • D) oscillation

    Answer: stabilization

    Explanation: Zener diode is used for voltage stabilization due to its constant voltage drop in reverse bias.

  9. Question 9

    Q9. The barrier potential in a p-n junction is

    • A) 0.1 V
    • B) 0.3 V
    • C) 0.7 V
    • D) 1.1 V

    Answer: 0.7 V

    Explanation: Barrier potential for Si is approximately 0.7 V.

  10. Question 10

    Q10. The common-mode rejection ratio (CMRR) of a differential amplifier is

    • A) the ratio of differential gain to common-mode gain
    • B) the ratio of common-mode gain to differential gain
    • C) the sum of differential and common-mode gains
    • D) the difference of differential and common-mode gains

    Answer: the ratio of differential gain to common-mode gain

    Explanation: CMRR = Ad / Ac, where Ad is differential gain and Ac is common-mode gain.

  11. Question 11

    Q11. The input impedance of a FET is

    • A) low
    • B) high
    • C) moderate
    • D) very low

    Answer: high

    Explanation: FET has high input impedance due to its insulated gate.

  12. Question 12

    Q12. The output of a logic gate is 1 when both inputs are 0. The gate is

    • A) AND
    • B) NAND
    • C) NOR
    • D) XNOR

    Answer: NAND

    Explanation: NAND gate produces 1 output when both inputs are 0.

  13. Question 13

    Q13. A silicon diode is forward-biased with a voltage of 0.7 V. The current is 10 mA. The dynamic resistance is

    • A) 25 Ω
    • B) 2.5 Ω
    • C) 50 Ω
    • D) 5 Ω

    Answer: 2.5 Ω

    Explanation: Dynamic resistance = ηVt / I = 25 mV / 10 mA = 2.5 Ω.

  14. Question 14

    Q14. The gain-bandwidth product of an amplifier is

    • A) constant
    • B) variable
    • C) dependent on feedback
    • D) proportional to gain

    Answer: constant

    Explanation: Gain-bandwidth product is a constant for an amplifier.

  15. Question 15

    Q15. The collector current in a transistor is 10 mA. If 90% of the electrons emitted reach the collector, the emitter current is

    • A) 11.11 mA
    • B) 12 mA
    • C) 9 mA
    • D) 8 mA

    Answer: 11.11 mA

    Explanation: Ie = Ic / 0.9 = 10 mA / 0.9 = 11.11 mA.

  16. Question 16

    Q16. The voltage gain of a CE amplifier with a load resistance of 1 kΩ is 100. If the load resistance is increased to 2 kΩ, the voltage gain becomes

    • A) 50
    • B) 200
    • C) 100
    • D) 400

    Answer: 200

    Explanation: Voltage gain is proportional to load resistance, hence gain doubles when Rl is doubled.

  17. Question 17

    Q17. The current gain of a transistor is 50. If the base current is 50 μA, the collector current is

    • A) 2.5 mA
    • B) 5 mA
    • C) 1 mA
    • D) 0.5 mA

    Answer: 2.5 mA

    Explanation: Ic = β * Ib = 50 * 50 μA = 2.5 mA.

  18. Question 18

    Q18. In a p-n junction, the depletion region is due to

    • A) majority carriers
    • B) minority carriers
    • C) immobile ions
    • D) recombination of carriers

    Answer: immobile ions

    Explanation: Depletion region is formed due to immobile ions left behind after recombination of majority carriers.

  19. Question 19

    Q19. The current gain of a transistor in CE mode is

    • A) always less than 1
    • B) always greater than 1
    • C) equal to 1
    • D) may be less or greater than 1

    Answer: always greater than 1

    Explanation: In CE mode, current gain (β) = ΔIc / ΔIb, which is typically greater than 1.

  20. Question 20

    Q20. The output of a logic gate is 1 when all its inputs are 0. The gate is

    • A) AND
    • B) NAND
    • C) NOR
    • D) OR

    Answer: NAND

    Explanation: NAND gate produces output 1 when all inputs are 0, as per its truth table.