Electronics (ECE) — MCQ Practice Questions & Answers

Question 1

In a common emitter amplifier, the voltage gain is maximum when the load resistance is

Accepted Answer

Correct answer: C. Much larger than output impedance — Voltage gain AV = gm × RL. Maximum gain occurs when load resistance is much larger than the output impedance of the transistor, limited only by practical considerations.

Answer

A. Very small

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B. Equal to output impedance

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D. Zero

Question 2

The input impedance of a common base amplifier is

Accepted Answer

Correct answer: B. Very low (Ω range) — Common base configuration has very low input impedance (typically 20-100 Ω) because the input is at the emitter which is forward biased.

Answer

A. Very high (MΩ range)

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C. Moderate (kΩ range)

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D. Frequency dependent

Question 3

For maximum power transfer in an amplifier circuit, the load impedance should be

Accepted Answer

Correct answer: B. Complex conjugate of source impedance — Maximum power transfer theorem states that maximum power is delivered when load impedance is the complex conjugate of source impedance (ZL = ZS*).

Answer

A. Equal to source impedance

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C. Much larger than source impedance

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D. Much smaller than source impedance

Question 4

The bandwidth of a common emitter amplifier can be increased by

Accepted Answer

Correct answer: D. Using emitter degeneration resistor without bypass capacitor — Emitter degeneration without bypass capacitor increases input impedance and reduces gain but significantly increases bandwidth due to negative feedback.

Answer

A. Increasing the load resistance

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B. Decreasing the emitter bypass capacitor

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C. Increasing the collector supply voltage

Question 5

In a differential amplifier, the common mode rejection ratio (CMRR) is defined as

Accepted Answer

Correct answer: A. Ratio of differential gain to common mode gain — CMRR = Ad/Ac, where Ad is differential mode gain and Ac is common mode gain. High CMRR (>80dB typical) is desired to reject common mode noise.

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B. Ratio of common mode gain to differential gain

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C. Product of differential and common mode gains

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D. Sum of differential and common mode gains

Question 6

Which configuration provides the highest voltage gain among the three BJT amplifier configurations?

Accepted Answer

Correct answer: C. Common emitter — Common emitter provides both voltage and current gain with gain values typically 100-1000. CB provides only current gain, CC provides only voltage gain close to 1.

Answer

A. Common base

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B. Common collector

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D. All provide same gain

Question 7

The input impedance of a voltage follower (common collector) amplifier is

Accepted Answer

Correct answer: B. Very high (MΩ range) — CC amplifier has very high input impedance (Zin ≈ β·re) making it suitable as a buffer stage between high impedance sources and low impedance loads.

Answer

A. Very low

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C. Equal to load impedance

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D. Independent of load resistance

Question 8

At what frequency does the gain of a RC coupled amplifier reduce to 70.7% of its mid-band gain?

Accepted Answer

Correct answer: B. At cutoff frequency (-3dB point) — The -3dB cutoff frequency is where the magnitude of gain reduces to 1/√2 (≈ 70.7%) of maximum gain. This defines the bandwidth of the amplifier.

Answer

A. At DC

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C. At twice the cutoff frequency

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D. At half the cutoff frequency

Electronics (ECE) - MCQ Practice Questions