A combinational circuit has 6 input variables. The minimum number of rows required in its truth table is:

The correct answer is B: 64. For n input variables, truth table rows = 2^n. For 6 inputs: 2^6 = 64 rows.

In a J-K flip-flop, when J=1 and K=1, the output will:

The correct answer is B: Toggle. When J=1 and K=1, the J-K flip-flop toggles its state on each clock pulse.

Which characteristic distinguishes CMOS gates from TTL gates in practical applications?

The correct answer is C: Lower power dissipation at rest. CMOS gates consume minimal static power (only during transitions), making them ideal for battery-operated and portable applications.

A circuit has a loop containing 5V source, 10V source (opposite polarity), 2Ω, and 3Ω resistors. Using KVL, the current magnitude in the loop is:

The correct answer is A: 1A. Applying KVL around loop: 5 - 10 + 2I + 3I = 0 (taking voltages in one direction). This gives -5 + 5I = 0, so I = 1A.

Which type of ADC provides the fastest conversion?

The correct answer is C: Flash ADC. Flash ADC uses parallel comparators and provides the fastest conversion as it converts in a single clock pulse, though at higher cost and power consumption.

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Electrical Engg (EEE)
Power Electronics

Electrical machines, power systems, circuits

49 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–49 of 49

Topics in Electrical Engg (EEE)

All Circuit Analysis 100 Electrical Machines 100 Power Systems 100 Control Systems 100 Power Electronics 100 Electrical Measurements 40 Digital Electronics 100

Q.41 Medium Power Electronics

The reverse recovery time of a diode is critical in power electronics because it:

A Determines the maximum frequency of operation

B Increases the forward voltage drop

C Reduces the efficiency of the converter

D All of the above

Correct Answer: D. All of the above

EXPLANATION

Reverse recovery time affects switching frequency limits, causes switching losses, and creates EMI. Fast recovery diodes are preferred in high-frequency applications.

Test

Q.42 Medium Power Electronics

The commutation of a thyristor in a circuit means:

A Turning it on

B Changing its gate signal polarity

C Turning it off by making anode current zero

D Increasing its temperature

Correct Answer: C. Turning it off by making anode current zero

EXPLANATION

Commutation is the process of turning off a thyristor by reducing anode current to below holding current value (natural commutation in AC circuits or forced commutation in DC).

Test

Q.43 Medium Power Electronics

A PWM (Pulse Width Modulation) controlled DC motor drive uses which power electronic device?

A Diode bridge

B Step-up transformer

C MOSFET or IGBT chopper

D Fixed resistor

Correct Answer: C. MOSFET or IGBT chopper

EXPLANATION

PWM control of DC motors uses switching devices like MOSFETs or IGBTs in chopper configuration to vary average voltage and control speed.

Test

Q.44 Medium Power Electronics

The holding current of an SCR is important because:

A It determines the forward voltage drop

B It is the minimum anode current required to keep SCR conducting

C It increases with temperature

D It reduces switching losses

Correct Answer: B. It is the minimum anode current required to keep SCR conducting

EXPLANATION

Holding current (Ih) is the minimum anode current below which SCR turns off. If Ia < Ih, SCR will not remain in conducting state.

Test

Q.45 Medium Power Electronics

A 3-phase diode rectifier (6-pulse) produces a ripple frequency of:

A 60 Hz (for 50 Hz supply)

B 100 Hz (for 50 Hz supply)

C 150 Hz (for 50 Hz supply)

D 300 Hz (for 50 Hz supply)

Correct Answer: C. 150 Hz (for 50 Hz supply)

EXPLANATION

For a 3-phase 6-pulse rectifier: Ripple frequency = 6 × supply frequency = 6 × 50 = 300 Hz (or 6 × 60 = 360 Hz for 60 Hz supply).

Test

Q.46 Medium Power Electronics

The switching frequency of power electronic devices is increased to:

A Reduce heat dissipation

B Reduce size of passive components

C Increase efficiency

D Reduce switching losses

Correct Answer: B. Reduce size of passive components

EXPLANATION

Higher switching frequency allows use of smaller inductors and capacitors, reducing converter size. Trade-off is increased switching losses.

Test

Q.47 Medium Power Electronics

In a step-down DC-DC converter (buck converter), the output voltage is always:

A Equal to input voltage

B Less than input voltage

C Greater than input voltage

D Zero

Correct Answer: B. Less than input voltage

EXPLANATION

A buck converter reduces voltage. Output voltage Vo = D × Vin, where D is duty cycle (0 < D < 1). For step-up, use boost converter.

Test

Q.48 Medium Power Electronics

Which of the following thyristors can be turned off by a gate signal?

A SCR (Silicon Controlled Rectifier)

B GTO (Gate Turn-off Thyristor)

C Triac

D Diac

Correct Answer: B. GTO (Gate Turn-off Thyristor)

EXPLANATION

GTO can be turned on and off by gate signals. SCR can only be turned on by gate signal; turn-off requires anode current to become zero.

Test

Q.49 Medium Power Electronics

A single-phase full-wave bridge rectifier with a 230V AC input produces an average output voltage of approximately:

A 103 V

B 163 V

C 207 V

D 325 V

Correct Answer: C. 207 V

EXPLANATION

For a full-wave rectifier: Vdc = (2√2/π) × Vrms = 0.9 × Vrms = 0.9 × 230 = 207 V approximately.

Test

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Electrical Engg (EEE) Power Electronics

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Power Electronics