All Free Electrical Engineering MCQs with Answers
Every Electrical Engineering question in the bank, across all chapters, each with the correct answer and a written explanation. Free and unlimited, with no account needed.
3,143 questions · page 141 of 158
- A. 30° to 150°.
- B. 30° to 180°.
- C. 60° to 120°.
- D. 60° to 180°.
Explanation: Current can begin when 400 sin α=200, giving α=30°. It can continue until the source again falls to 200 V at 150°, so the control range is…
Correct answer: 30° to 150°.- A. RL.
- B. RLC underdamped.
- C. RLC overdamped.
- D. RLC critically damped
Explanation: Load commutation needs the load itself to provide a reverse current or voltage for turning off the thyristor.
Correct answer: RLC underdamped.- A. it can be turned OFF but not ON with a gate pulse.
- B. it conducts only during one half cycle of an alternating current wave.
- C. it can be turned ON but not OFF with a gate pulse.
- D. it can be turned ON only during one half cycle of an AC.
Explanation: A gate pulse can trigger an SCR into conduction, but removing the gate signal does not turn it off.
Correct answer: it can be turned ON but not OFF with a gate pulse.- A. 1500 A.
- B. 6000 A.
- C. 2121.32 A.
- D. 4242.64 A.
Explanation: For the same I²t surge-energy limit, doubling the conduction time reduces the allowable current by √2.
Correct answer: 2121.32 A.- A. Drain, source, gate
- B. Two main terminal and a gate terminal
- C. Cathode, anode, gate
- D. None of the above
Explanation: A TRIAC is a bidirectional thyristor with two main terminals, MT1 and MT2, plus a gate terminal.
Correct answer: Two main terminal and a gate terminal- A. PNPN device
- B. A combination of diac and triac
- C. A set of SCRs
- D. A set if SCR,diac and triac
Explanation: A thyristor has four semiconductor layers arranged as P-N-P-N, giving it three junctions.
Correct answer: PNPN device- A. Diac
- B. Triac
- C. SUS
- D. BCS
Explanation: A BCS, or bilateral controlled switch, is a PNPN-type device controlled through two gates.
Correct answer: BCS- A. Unijunction device
- B. Device with three junction
- C. Device with four junction
- D. None of the above
Explanation: An SCR contains four layers, PNPN, and therefore has three internal PN junctions.
Correct answer: Device with three junction- A. Diac
- B. Triac
- C. Silicon controlled-rectifier SCR
- D. None of above
Explanation: A thyratron is a gas-filled switching tube, and its semiconductor counterpart is the silicon-controlled rectifier, or SCR.
Correct answer: Silicon controlled-rectifier SCR- A. Above 220 kv
- B. Above 11kv
- C. Below 660 v
- D. Below 115 v
Explanation: Solid grounding is generally used on low-voltage systems, where the neutral is directly connected to earth and fault current can be safely…
Correct answer: Below 660 v- A. D.C voltage
- B. A.C voltage
- C. Half A.C voltage
- D. Half D.C voltageGet Study Guides
Explanation: AC voltage can be stepped up or down easily with transformers. High-voltage AC transmission carries the same power at lower current…
Correct answer: A.C voltage- A. 200 V D.C.
- B. 25 kV single phase A.C.
- C. 25 kV two phase A.C.
- D. 25 kV three phase A.C.
Explanation: The standard main-line railway electrification system for long-distance routes is 25 kV, single-phase AC at 50 Hz.
Correct answer: 25 kV single phase A.C.- A. ground fault on a cable
- B. short circuit fault on a cable
- C. both the ground fault and the short-circuit fault
- D. none of the above
Explanation: The Murray loop test uses a healthy conductor and a bridge arrangement to locate low-resistance faults such as earth faults and…
Correct answer: both the ground fault and the short-circuit fault- A. Adjustment of voltage at consumers premises within statutory limits
- B. Control of active and reactive power
- C. Adjustment of short period daily and seasonal voltage variations in accordance with variations of load
- D. All of the above
Explanation: Voltage control keeps consumer voltage within statutory limits, compensates for daily and seasonal load variations, and helps regulate…
Correct answer: All of the above- A. overhead telephone wire
- B. earth wire
- C. core wire of ACSR
- D. all of the above
Explanation: Steel provides high mechanical strength, so it is used for overhead telephone wires, earth wires, and the central reinforcing core of ACSR…
Correct answer: all of the above- A. Copper
- B. Aluminium
- C. Steel reinforced copper
- D. Steel reinforced aluminium
Explanation: Steel-reinforced aluminium conductors combine aluminium's low weight and good conductivity with steel's mechanical strength, making them…
Correct answer: Steel reinforced aluminium- A. Increases
- B. Decreases
- C. Remains unaffected
Explanation: In an ungrounded system, a single line-to-ground fault shifts the neutral potential.
Correct answer: Increases- A. transmission line
- B. motor
- C. generator
- D. feeder
Explanation: Transmission-line design must limit I²R losses because these losses waste generated power and reduce transmission efficiency.
Correct answer: transmission line- A. connecting lines in parallel
- B. connecting lines in series
- C. using machines of high impedance
- D. reducing the excitation of machines
- E. none of the above
Explanation: Parallel lines reduce the equivalent transfer reactance and increase the maximum power transfer, since Pmax is inversely proportional to…
Correct answer: connecting lines in parallel- A. compensate for line inductive reactance
- B. compensate for line capacitive reactance
- C. improve line voltage
- D. none of the above
Explanation: A series capacitor supplies capacitive reactance in series with the line, thereby cancelling part of the line's inductive reactance.
Correct answer: compensate for line inductive reactance