Transistor Amplifiers MCQs

Practice Transistor Amplifiers MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Analog ElectronicsTransistor Amplifiers

A common-emitter amplifier normally produces what phase difference between input and output voltage?

A0 degrees
B90 degrees
C180 degrees
D270 degrees

Show AnswerHide Answer Report an error

Correct Answer: C. 180 degrees

Explanation: A common-emitter voltage amplifier is inverting, giving approximately 180 degrees phase reversal.

Reference: Standard analog electronics: transistor amplifiers

Question 2

Analog ElectronicsTransistor Amplifiers

A common-collector amplifier is particularly useful as a?

AHigh-voltage-gain stage
BBuffer and impedance-matching stage
CRectifier
DHigh-frequency oscillator only

Show AnswerHide Answer Report an error

Correct Answer: B. Buffer and impedance-matching stage

Explanation: The emitter follower has high input resistance, low output resistance and voltage gain near unity.

Reference: Standard analog electronics: transistor amplifiers

Question 3

Analog ElectronicsTransistor Amplifiers

In a BJT amplifier operating in the active region, the base-emitter and base-collector junctions are respectively?

AForward biased
BReverse biased
CBoth forward biased
DBoth reverse biased

Show AnswerHide Answer Report an error

Correct Answer: A. Forward biased

Explanation: For normal amplification the base-emitter junction is forward biased and the base-collector junction is reverse biased.

Reference: Standard analog electronics: transistor amplifiers

Question 4

Analog ElectronicsTransistor Amplifiers

Which BJT configuration commonly provides both appreciable voltage gain and current gain?

ACommon base
BCommon emitter
CCommon collector
DEmitter follower only

Show AnswerHide Answer Report an error

Correct Answer: B. Common emitter

Explanation: The common-emitter configuration provides both voltage and current gain and is widely used for general amplification.

Reference: Standard analog electronics: transistor amplifiers

Question 5

Analog ElectronicsTransistor Amplifiers

A common-emitter amplifier has an approximate small-signal voltage gain Av = -gmRC. If gm = 40 mS and RC = 2 kOhm, neglecting loading and output resistance, Av is?

A-8
B-20
C-80
D-800

Show AnswerHide Answer Report an error

Correct Answer: C. -80

Explanation: Av ≈ -gmRC = -(0.04)(2000) = -80. The negative sign denotes phase inversion.

Reference: Standard analog electronics: transistor amplifiers

Question 6

Analog ElectronicsTransistor Amplifiers

A BJT biased at IC = 2 mA has transconductance gm approximately equal to what, using VT = 25 mV?

A8 mS
B20 mS
C40 mS
D80 mS

Show AnswerHide Answer Report an error

Correct Answer: D. 80 mS

Explanation: gm = IC/VT = 0.002/0.025 = 0.08 S = 80 mS.

Reference: Standard analog electronics: transistor amplifiers

Question 7

Analog ElectronicsTransistor Amplifiers

For a BJT with beta = 100 and gm = 50 mS, the hybrid-pi input resistance r_pi is approximately?

A200 ohm
B2 kOhm
C5 kOhm
D50 kOhm

Show AnswerHide Answer Report an error

Correct Answer: B. 2 kOhm

Explanation: r_pi = beta/gm = 100/0.05 = 2000 ohm = 2 kOhm.

Reference: Standard analog electronics: transistor amplifiers

Question 8

Analog ElectronicsTransistor Amplifiers

The Early effect in a BJT causes collector current in the active region to?

ABe completely independent of VCE
BIncrease somewhat as VCE increases at fixed base drive
CBecome exactly zero
DReverse direction at all times

Show AnswerHide Answer Report an error

Correct Answer: B. Increase somewhat as VCE increases at fixed base drive

Explanation: Base-width modulation causes collector current to depend slightly on collector-emitter voltage, giving a finite transistor output resistance.

Reference: Standard analog electronics: transistor amplifiers

Question 9

Analog ElectronicsTransistor Amplifiers

In the hybrid-pi small-signal model, the BJT output resistance ro associated with the Early effect is approximately?

AVA/IC
BIC/VA
Cbeta times IC
DVT times IC

Show AnswerHide Answer Report an error

Correct Answer: A. VA/IC

Explanation: For a transistor biased in active region, ro is commonly approximated as VA/IC, where VA is the Early voltage.

Reference: Standard analog electronics: transistor amplifiers

Question 10

Analog ElectronicsTransistor Amplifiers

A BJT has Early voltage VA = 100 V and IC = 1 mA. Its small-signal output resistance ro is approximately?

A1 kOhm
B10 kOhm
C100 kOhm
D1 MOhm

Show AnswerHide Answer Report an error

Correct Answer: C. 100 kOhm

Explanation: ro ≈ VA/IC = 100 V / 0.001 A = 100 kOhm.

Reference: Standard analog electronics: transistor amplifiers

Question 11

Analog ElectronicsTransistor Amplifiers

A common-emitter amplifier has gm = 25 mS and an effective collector load of 4 kOhm. Neglecting emitter degeneration and output resistance, its voltage gain is approximately?

A-10
B-25
C-100
D-160

Show AnswerHide Answer Report an error

Correct Answer: C. -100

Explanation: For the simplified small-signal model, Av ≈ -gmRL = -(0.025)(4000) = -100.

Reference: Standard analog electronics: transistor amplifiers

Question 12

Analog ElectronicsTransistor Amplifiers

A BJT is biased at IC = 2.5 mA. Using VT = 25 mV, its intrinsic emitter small-signal resistance re ≈ VT/IE is closest to?

A1 ohm
B10 ohm
C100 ohm
D1 kOhm

Show AnswerHide Answer Report an error

Correct Answer: B. 10 ohm

Explanation: With IE approximately equal to IC, re ≈ 25 mV/2.5 mA = 10 ohm.

Reference: Standard analog electronics: transistor amplifiers

Question 13

Analog ElectronicsTransistor Amplifiers

A common-emitter stage has an unbypassed emitter resistance RE = 1 kOhm and small-signal emitter resistance re = 25 ohm. Neglecting other effects, the emitter degeneration is dominated by?

AThe 25 ohm intrinsic resistance only
BThe 1 kOhm external emitter resistor
CCollector-base capacitance only
DSupply resistance only

Show AnswerHide Answer Report an error

Correct Answer: B. The 1 kOhm external emitter resistor

Explanation: Because RE is much larger than re, the external emitter resistance dominates the emitter degeneration and strongly reduces gain sensitivity.

Reference: Standard analog electronics: transistor amplifiers