Electronics mcqs

BASIC ELECTRONICS MCQs 3

BASIC ELECTRONICS MCQs 3

Q.1 If the output voltage of a bridge rectifier is 100V, the PIV of diode will be

  • (A) 100√2V
  • (B) 200/πV
  • (C) 100πV
  • (D) 100π/2 V

Ans. (D)

Peak inverse voltage = max secondary voltage

Vdc=2Vm/ π=100

Vm=100 π/2

Q.2 In the voltage regulator shown below, if the current through the load decreases,

  • (A) The current through R1 will increase.
  • (B) The current through R1 will decrease.
  • (C) zener diode current will increase.
  • (D) zener diode current will decrease.

Ans. (C)

Q.3 In Boolean algebra A + AB

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

Ans. (A)

A.1+A B= A (1+B) +A B = A + AB +A B = A+B (A +A) = A+B

Q.4 For a JFET, when VDS is increased beyond the pinch off voltage, the drain current

  • (A) Increases
  • (B) Decreases
  • (C) Remains constant.
  • (D) First decreases and then increases.

Ans. (C)

At pinch off voltage drain current reaches its maximum off. Now if we further increase VDS above Vp the depletion layer expands at the top of the channel. The channel acts as a current limiter & holds drain current constant.

Q.5 The type of power amplifier which exhibits crossover distortion in its output is

  • (A) Class A
  • (B) Class B
  • (C) Class AB
  • (D) Class C

Ans. (B)

The transistors do not conduct until the input signal is more than cut-in voltage of the BA junction. In class B, the devices being biased atcut-off, one device stops conducting before the other device starts conducting leaving to Cross-over distortion.

Q.6 The main advantage of a crystal oscillator is that its output is

  • (A) 50Hz to 60Hz
  • (B) Variable frequency
  • (C) A constant frequency.
  • (D) d.c

Ans. (C)

The quality factor (Q) of a crystal as a resonating element is very high, of the order of thousands. Hence frequency of a crystal oscillator is highly stable.

Q.7 The lowest output impedance is obtained in case of BJT amplifiers for

  • (A) CB configuration.
  • (B) CE configuration.
  • (C) CC configuration.
  • (D) CE with RE configuration.

Ans. (C)

The output impedance in case of CC configuration is on the order of a few ohms. (In case of CB ≈450kΩand in case of CE ≈45kΩ)

Q.8 N-channel FETs are superior to P-channel FETs, because

  • (A) They have higher input impedance
  • (B) They have high switching time
  • (C) They consume less power
  • (D) Mobility of electrons is greater than that of holes

Ans. (D)

Q.9 The upper cutoff frequency of an RC coupled amplifier mainly depends upon

  • (A) Coupling capacitor
  • (B) Emitter bypass capacitor
  • (C) Output capacitance of signal source
  • (D) Inter-electrode capacitance and stray shunt capacitance

Ans. (D)

Q.10 Just as a voltage amplifier amplifies signal-voltage, a power amplifier

  • (A) Amplifies power
  • (B) Amplifies signal current
  • (C) Merely converts the signal ac power into the dc power
  • (D) Merely converts the dc power into useful ac power

Ans. (D)

Q.11 A radio frequency signal contains three frequency components, 870 KHz, 875 KHz and 880 KHz. The signal needs to be amplified. The amplifier used should be

  • (A) audio frequency amplifier
  • (B) Wide band amplifier
  • (C) Tuned voltage amplifier
  • (D) Push-pull amplifier

Ans. (C)

We need to amplify 3 signal frequencies i.e., 870 kHz, 875 kHz and 880 kHz. These frequencies lie in a bandwidth of 10 kHz and we should use only tuned voltage amplifiers to amplify them.

Q.12 An oscillator of the LC type that has a split capacitor in the circuit is

  • (A) Hartley oscillator
  • (B) Colpitts oscillator
  • (C) Weinbridge oscillator
  • (D) R-C phase shift oscillator

Ans. (B)

We have two capacitors in the tank circuit, which serve as a simple ac voltage divider.

Q.13 The function of a bleeder resistor in a power supply is

  • (A) The same as that of load resistor
  • (B) To ensure a minimum current drain in the circuit
  • (C) To increase the output dc voltage
  • (D) To increase the output current

Ans. (B)

Q.14 In a bistable multivibrator circuit, commutating capacitor is used

  • (A) To increase the base storage charge
  • (B) To provide ac coupling
  • (C) To increase the speed of response
  • (D) To provide the speed of oscillations

Ans. (C)

The commutating capacitor is used for the speedy transition of the state of the bistable.

Q.15 n-type silicon is obtained by

  • (A) Doping with tetravalent element
  • (B) Doping with pentavalent element
  • (C) Doping with trivalent element
  • (D) Doping with a mixture of trivalent and tetravalentelement

Ans: (B)

The pentavalent atom provides an excess electronwhile the other four form the covalent bond with the neighbouring atoms. This excess free electron provides the n type conductivity.

Q.16 The forward characteristic of a diode has a slope of approximately 50mA/V at a desired point. The approximate incremental resistance of the diode is

  • (A) 50Ω
  • (B) 35Ω
  • (C) 20Ω
  • (D) 10Ω

Ans: (C)

Resistance at any point in the forward characteristics is given by R= ∆V/ ∆I = 1/50mA = 20Ω

Q.17 Two stages of BJT amplifiers are cascaded by RC coupling. The voltage gain of the first stage is 10 and that of the second stage is 20. The overall gain of the coupled amplifier is

  • (A) 10×20
  • (B) 10+20
  • (C) (10+20)2
  • (D) (10×20)/2

Ans: (A)

The voltage gain of a multistage amplifier is equal to the product of the gains of the individual stages.

Q.18 In the voltage range, Vp < VDS< BVDSS of an ideal JFET or MOSFET

  • (A) The drain current varies linearly with VDS.
  • (B) The drain current is constant.
  • (C) The drain current varies nonlinearly with VDS.
  • (D) The drain current is cut off.

Ans: (B)

It is the saturation region or pinch off region, and drain current remains almost constant at its maximum value, provided VGS is kept constant.

Q.19 In a voltage shunt negative feedback amplifier system, the input resistance Ri and the output resistance Ro of the basic amplifier are modified as follows:

  • (A) Ri is decreased and Ro increased.
  • (B) Both Ri and Ro are decreased.
  • (C) Both Ri and Ro are increased
  • (D) Ri is increased and Ro is decreased.

Ans: (B)

Here, a fraction of output voltage obtained by parallel sampling is applied in parallel with the input voltage through feedback and both input and output resistance decrease by a factor equal to (1+ βAv).

Q.20 The use of crystal in a tunable oscillator

  • (A) Improves frequency stability.
  • (B) Increases the gain of the oscillator.
  • (C) Helps to obtain optimum output impedance.
  • (D) Facilitates generation of wide range of frequencies.

Ans: (A)

Piezoelectric crystal is used as a resonant tank circuit. The crystal is made of quartz material and provides a high degree of frequency stability.

(BASIC ELECTRONICS MCQs 3)