BJT Biasing MCQs

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

Question 1

Electronic Devices & CircuitsBJT Biasing

In a DC load-line analysis of a common-emitter transistor circuit, the Q-point represents?

AThe maximum supply voltage only
BThe quiescent DC operating point
CThe transistor breakdown point only
DThe AC frequency response

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Correct Answer: B. The quiescent DC operating point

Explanation: The Q-point specifies the transistor's steady DC collector current and collector-emitter voltage with no input signal applied.

Reference: Standard analog electronics: transistor biasing

Question 2

Electronic Devices & CircuitsBJT Biasing

For symmetrical maximum undistorted voltage swing in a simple class-A common-emitter stage, the Q-point is commonly chosen near?

ACutoff only
BSaturation only
CThe middle of the DC load line
DZero collector current and zero VCE simultaneously

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Correct Answer: C. The middle of the DC load line

Explanation: Biasing near the center of the DC load line allows approximately equal signal swing toward cutoff and saturation.

Reference: Standard analog electronics: Q-point selection

Question 3

Electronic Devices & CircuitsBJT Biasing

A BJT has VCC = 10 V, RC = 2 kOhm and collector current IC = 2 mA. Neglecting emitter resistance, VCE is approximately?

A2 V
B4 V
C6 V
D10 V

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Correct Answer: C. 6 V

Explanation: The drop across RC is IC RC = 2 mA × 2 kOhm = 4 V. Thus VCE ≈ 10 - 4 = 6 V.

Reference: Standard transistor bias: collector circuit calculation

Question 4

Electronic Devices & CircuitsBJT Biasing

For a fixed-bias NPN transistor with VCC = 10 V, RB = 470 kOhm, emitter grounded and VBE = 0.7 V, the base current is closest to?

A2 microampere
B20 microampere
C200 microampere
D2 mA

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Correct Answer: B. 20 microampere

Explanation: IB = (VCC - VBE)/RB = 9.3 V / 470 kOhm ≈ 19.8 microampere, about 20 microampere.

Reference: Standard transistor bias calculation

Question 5

Electronic Devices & CircuitsBJT Biasing

If the transistor in the previous type of fixed-bias circuit has beta = 100 and IB = 20 microampere while remaining in active region, IC is approximately?

A0.2 mA
B2 mA
C20 mA
D200 mA

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Correct Answer: B. 2 mA

Explanation: IC = beta IB = 100 × 20 microampere = 2 mA.

Reference: Standard transistor bias calculation

Question 6

Electronic Devices & CircuitsBJT Biasing

Thermal runaway in a BJT refers to a potentially destructive process in which?

AIncreasing temperature can increase collector current and power dissipation, causing further heating
BThe transistor temperature always falls as current rises
CBase current becomes exactly zero at all temperatures
DThe collector-emitter voltage becomes an AC waveform only

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Correct Answer: A. Increasing temperature can increase collector current and power dissipation, causing further heating

Explanation: Temperature-dependent increases in leakage/current can raise power dissipation, causing additional heating and potentially a regenerative failure process if bias is not stabilized.

Reference: Standard transistor electronics: thermal stability

Question 7

Electronic Devices & CircuitsBJT Biasing

Which BJT bias arrangement is generally more stable against beta variation than simple fixed-base bias?

AVoltage-divider bias with emitter resistance
BFixed-base bias with no emitter resistor
CCollector left open
DBase and collector both grounded

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Correct Answer: A. Voltage-divider bias with emitter resistance

Explanation: Voltage-divider bias combined with emitter feedback makes the operating point less dependent on transistor beta than simple fixed-base bias.

Reference: Standard analog electronics: voltage-divider bias

Question 8

Electronic Devices & CircuitsBJT Biasing

Thermal runaway in a BJT bias circuit is associated with a self-reinforcing rise in collector current caused by?

ATemperature-dependent device changes and increased power dissipation
BA decrease in temperature to absolute zero
CAn ideal current source with infinite compliance
DA disconnected power supply

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Correct Answer: A. Temperature-dependent device changes and increased power dissipation

Explanation: Higher junction temperature can increase leakage and alter VBE-related current, increasing dissipation and temperature further unless bias stabilization limits the process.

Reference: Standard transistor electronics: thermal runaway

Question 9

Electronic Devices & CircuitsBJT Biasing

Emitter resistance in a BJT bias circuit improves thermal stability mainly by providing?

ANegative feedback against increases in emitter and collector current
BPositive feedback that increases current indefinitely
COptical isolation
DA higher transistor breakdown voltage directly

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Correct Answer: A. Negative feedback against increases in emitter and collector current

Explanation: If current rises, the emitter voltage rises across RE, reducing effective base-emitter drive and opposing the current increase.

Reference: Standard transistor electronics: emitter degeneration and bias stability