PlacementPrepIn a forward-biased silicon diode, the approximate cut-in voltage is:
Solution
Silicon diodes start conducting at about 0.7 V; germanium at about 0.3 V.
Answer: (D) 0.7 V
Technical · Electronics and Communication (ECE)
Analog Electronics MCQs for placement tests
20 technical questions of moderate difficulty, as asked in campus placement and company tests. Each has a short explanation.
A Zener diode is mainly used as a:
Solution
In reverse breakdown it holds a nearly constant voltage.
Answer: (B) Voltage regulator
The ripple factor of a full-wave rectifier (without filter) is about:
Solution
The ripple factor is 1.21 for half-wave and 0.48 for full-wave.
Answer: (C) 0.48
Which BJT configuration gives the highest voltage gain along with a phase shift of 180°?
Solution
The common-emitter amplifier inverts the signal and has high voltage gain.
Answer: (B) Common emitter
A common collector amplifier is also called:
Solution
Its voltage gain is close to 1 and the output follows the input.
Answer: (D) An emitter follower
For a BJT, if β = 100 and the base current is 20 µA, the collector current is:
Solution
Ic = β × Ib = 100 × 20 µA = 2 mA.
Answer: (D) 2 mA
An ideal op-amp has:
Solution
Ideal op-amps also have infinite open-loop gain and bandwidth.
Answer: (D) Infinite input impedance and zero output impedance
The gain of an inverting amplifier with Rf = 100 kΩ and Rin = 10 kΩ is:
Solution
Gain = −Rf / Rin = −10.
Answer: (D) −10
The gain of a non-inverting amplifier with Rf = 90 kΩ and R1 = 10 kΩ is:
Solution
Gain = 1 + Rf / R1 = 1 + 9 = 10.
Answer: (A) 10
Which oscillator uses an RC network to give 180° phase shift?
Solution
Three RC sections give 180°, and the transistor gives the other 180°.
Answer: (D) RC phase-shift oscillator
Barkhausen's criterion for sustained oscillation requires the loop gain to be:
Solution
|Aβ| = 1 and the phase shift around the loop is 0° (or 360°).
Answer: (B) Equal to 1 with a total phase shift of 0° or 360°
Which amplifier class has the highest efficiency?
Solution
Class C conducts for less than half the cycle and can exceed 75% efficiency.
Answer: (D) Class C
The maximum theoretical efficiency of a class B push-pull amplifier is:
Solution
π/4 ≈ 78.5%.
Answer: (D) 78.5%
A MOSFET is a:
Solution
The gate voltage controls the drain current.
Answer: (C) Voltage-controlled device
Negative feedback in an amplifier:
Solution
It trades gain for stability, wider bandwidth and lower distortion.
Answer: (B) Reduces gain but improves stability and bandwidth
The CMRR of a differential amplifier should ideally be:
Solution
A high common-mode rejection ratio means common-mode signals are rejected.
Answer: (B) Infinite
In a bridge rectifier, how many diodes conduct during each half cycle?
Solution
Two diodes in series conduct in each half cycle.
Answer: (A) 2
The peak inverse voltage across each diode in a bridge rectifier is:
Solution
In a bridge rectifier, each non-conducting diode sees the peak voltage Vm.
Answer: (C) Vm
An LED emits light when it is:
Solution
Electrons recombine with holes and release energy as light.
Answer: (A) Forward biased
A capacitor filter after a rectifier mainly:
Solution
The capacitor charges to the peak and discharges slowly, smoothing the output.
Answer: (A) Reduces ripple
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