Free Electrical Machines MCQs with Answers
1,061 Electrical Machines MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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- A. thick wire placed at the bottom of the slots
- B. thick wire placed at the top of the slots
- C. thin wire placed at the top of the slots
- D. thin wire placed at the bottom of the slots
Explanation: The auxiliary winding uses thin, high-resistance wire and is placed toward the top of the slots, while the main winding uses thicker wire.
Correct answer: thin wire placed at the top of the slots- A. 0.6 power factor lagging
- B. 0.8 power factor lagging
- C. 0.8 power factor leading
- D. unity power factor
Explanation: A single-phase induction motor normally draws magnetizing current and therefore operates with a lagging power factor, commonly around 0.6…
Correct answer: 0.6 power factor lagging- A. Shaped pole motor
- B. Split phase motor
- C. Capacitor start motor
- D. Capacitor run motor
Explanation: The running capacitor remains in circuit in a capacitor-run motor and continuously supplies reactive current, improving the phase…
Correct answer: Capacitor run motor- A. Reluctance motor
- B. Series motor
- C. Repulsion motor
- D. Universal motor
Explanation: A reluctance motor is valued for nearly constant speed and simple, reliable operation, making it suitable for timing devices and control…
Correct answer: Reluctance motor- A. zero slip
- B. negative slip
- C. positive slip
- D. all of the above
Explanation: A Schrage motor permits operation below, at, or above synchronous speed, corresponding respectively to positive, zero, and negative slip.
Correct answer: all of the above- A. A.C. only
- B. D.C. only
- C. either A.C. or D.C.
- D. none of the above
Explanation: A universal motor has its field and armature connections arranged so that torque remains unidirectional with either supply type.
Correct answer: either A.C. or D.C.- A. Shaded pole motor
- B. Hysteresis motor
- C. Two value capacitor motor
- D. Universal motor
Explanation: A hysteresis motor runs smoothly and quietly at nearly constant speed, making it suitable for tape recorders and other timing…
Correct answer: Hysteresis motor- A. inherently self-starting with high torque
- B. inherently self-starting with low torque
- C. inherently non-self-starting with low torque
- D. inherently non-self-starting with high torque
Explanation: A single-phase induction motor produces a pulsating magnetic field whose forward and backward torque components cancel at standstill.
Correct answer: inherently non-self-starting with low torque- A. Electric shavers
- B. Refrigerators
- C. Signalling and timing devices
- D. Lifts and hoists
Explanation: Reluctance motors are valued for nearly constant speed and simple construction, so they are used in signalling, timing, and control…
Correct answer: Signalling and timing devices- A. universal motor
- B. D.C. shunt motor
- C. single-phase capacitor run motor
- D. 3-phase synchronous motor
Explanation: A capacitor-run motor provides reasonably good starting torque, smooth operation, and nearly constant speed, which suit small lathes.
Correct answer: single-phase capacitor run motor- A. hysteresis loss
- B. magnetisation of rotor
- C. eddy current loss
- D. electromagnetic induction
Explanation: A hysteresis motor develops torque because the rotor magnetisation lags the rotating stator field, producing hysteresis torque associated…
Correct answer: hysteresis loss- A. D.C. shunt motor
- B. Schrage motor
- C. Repulsion start and induction run motor
- D. Universal motor
Explanation: The Schrage motor has a series-type commutator construction that provides very high starting torque.
Correct answer: Schrage motor- A. lagging
- B. always leading
- C. unity
- D. unity to 0.8 leading
Explanation: The stator magnetising current of a single-phase induction motor lags the supply voltage, so its power factor is normally lagging.
Correct answer: lagging- A. toys
- B. hair dryers
- C. circulators
- D. any of the above
Explanation: Shaded-pole motors are inexpensive, compact, and suitable for small loads such as toys, hair dryers, and circulators.
Correct answer: any of the above595. In a capacitor start single-phase motor, when capacitor is replaced by a resistance____________?
- A. torque will increase
- B. the motor will consume less power
- C. motor will run in reverse direction
- D. motor will continue to run in same direction
Explanation: Replacing the capacitor with a resistance still creates a phase difference between the main and auxiliary winding currents, so the motor…
Correct answer: motor will continue to run in same direction- A. repulsion induction motor
- B. repulsion motor
- C. repulsion start induction run motor
- D. none of the above
Explanation: In a repulsion-start induction-run motor, the commutator and brushes provide repulsion starting torque, then a short-circuiter closes the…
Correct answer: repulsion start induction run motor- A. 95% to 99%
- B. 80% to 90%
- C. 50% to 75%
- D. 5% to 35%
Explanation: Shaded-pole motors have high rotor losses and weak starting torque, so their efficiency is very low, commonly about 5% to 35%.
Correct answer: 5% to 35%- A. short circuited capacitor
- B. capacitor value hiving changed
- C. open circuiting of capacitor
- D. none of the above
Explanation: A short-circuited capacitor removes the intended impedance and phase shift from the auxiliary circuit, causing excessive current in the…
Correct answer: short circuited capacitor- A. running winding only
- B. starting winding only
- C. either A. or (b)
- D. both A. and (b)
Explanation: The direction depends on the relative phase between the main and starting windings.
Correct answer: either A. or (b)- A. Split motor
- B. Shaded-pole motor
- C. Reluctance motor
- D. None of these
Explanation: A shaded-pole motor is inherently self-starting because the shading coil creates a weak sweeping magnetic field across each pole.
Correct answer: Shaded-pole motor