All Free Electrical Engineering MCQs with Answers

• A. High power phase control
• B. High power current control
• C. Low power current control
• D. Low power phase control

Explanation: A bidirectional controlled thyristor is intended for high-power AC control, especially phase-control applications such as AC voltage…

• A. Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3.
• B. Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3.
• C. Vc1 = Vc2 = Vc3 any value of Ig.
• D. Vc1 > Vc2 > Vc3 when Ig1 ≥ Ig2 &Atil

Explanation: Increasing gate current assists thyristor turn-on and reduces its forward breakover voltage. Thus, if Ig1 < Ig2 < Ig3, then Vc1 > Vc2 > Vc3.

• A. Forward voltage triggering
• B. Gate triggering
• C. dV / dt triggering
• D. Thermal triggering

Explanation: Gate triggering is the most reliable method because the gate provides deliberate, controlled turn-on with relatively low triggering power.

• A. forward blocking mode
• B. reverse blocking mode
• C. both forward and reverse blocking mode
• D. forward conduction mode

Explanation: A thyristor carries only leakage current in either blocking condition: forward blocking with the anode positive, or reverse blocking with…

• A. Recovery is only 5 µs
• B. Recovery is only 50 µs
• C. Doping is carried out
• D. None of these

Explanation: Fast recovery is obtained by lifetime-control techniques such as doping, but these introduce trade-offs including increased leakage…

• A. CB
• B. Snubber circuit
• C. Voltage clamping device
• D. Fast acting current limiting device (FACL fuse)

Explanation: A very large, short-duration surge current is limited by a fast-acting current-limiting fuse, which interrupts the fault before the…

• A. of long period
• B. of short duration
• C. both (A) and (B)
• D. neither (A) nor (B)

Explanation: A circuit breaker is relatively slow and is intended to clear sustained or long-duration overcurrent faults.

• A. 20 A
• B. 200 A
• C. 600 A
• D. 400 A

Explanation: A GTO typically requires a negative gate current of roughly 20–25% of its anode current for turn-off.

• A. CB and fuse.
• B. Heat sink.
• C. Snubber circuit.
• D. Voltage clamping device.

Explanation: Overcurrent protection for an SCR uses series protective devices such as fuses and circuit breakers.

• A. high value.
• B. low value.
• C. zero value.
• D. moderate value.

Explanation: A voltage-clamping device must draw negligible current during normal voltage, so it presents high impedance.

• A. low
• B. High
• C. moderate
• D. infinity

Explanation: During an overvoltage surge, a clamping device such as a MOV changes to a low-impedance state.

• A. 100 mA
• B. 500 mA
• C. 1 A
• D. 2 A

Explanation: The latching current of a GTO is generally in the hundreds-of-milliamperes range, and 500 mA is the suitable order among the choices.

• A. fast acting fuse
• B. snubber circuit
• C. metal oxide varistor
• D. aluminium block

Explanation: A metal-oxide varistor, or MOV, is a voltage-dependent resistor that remains high-impedance normally and conducts strongly during a…

• A. 5 KHz
• B. 10 KHz
• C. 60 KHz
• D. 100 KHz

Explanation: The static induction thyristor, or SITH, is designed for high-speed switching and can operate at frequencies of approximately 100 kHz.

• A. One resistor across the string
• B. Resistors of the same value across each SCR
• C. Resistors of different values across each SCR
• D. One resistor in series with each SCR

Explanation: Equal-value resistors connected across each series SCR share the steady-state voltage nearly equally, compensating for leakage-current…

• A. RL.
• B. RLC underdamped.
• C. RLC overdamped.
• D. RLC critically damped.

Explanation: Load commutation requires an RLC load whose response is oscillatory, allowing the load current to naturally fall to zero and reverse…

• A. junction J2 is in reverse bias and J1, J3 is in forward bias.
• B. junction J3 is in forward bias and J1, J2 is in reverse bias.
• C. Junction J1, J3 is in reverse bias and J2 is in forward bias.
• D. Junction J1 and J2 is in forward bias and J3 is in reverse bias.

Explanation: In forward blocking, the outer junctions J1 and J3 are forward biased while the central junction J2 is reverse biased.

• A. junction J2 is in reverse bias and J1, J3 is in forward bias.
• B. junction J3 is in forward bias and J1, J2 in reverse bias.
• C. junction J1, J3 is in reverse bias and J2 is in forward bias.
• D. junction J1 and J2 is in forward bias and J3 is in reverse bias.

Explanation: With reverse voltage applied, J1 and J3 are reverse biased and J2 is forward biased.

• A. It is related to turn off process of the device.
• B. It is related to conduction process of device.
• C. It is related to turn on process of the device.
• D. Both C and D.

Explanation: Latching current concerns the turn-on transition: after the gate pulse is removed, the anode current must rise above this value to latch…

• A. 0.32
• B. 0.67
• C. 0.45
• D. 0.27

Explanation: For an ideal step-up chopper, V_o=V_s/(1-D). Thus D=1-110/150=0.267, approximately 0.27; the larger duty-cycle values would produce much…