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. heavy
- B. medium
- C. normal
- D. low
Explanation: A jaw crusher must break and compress hard material, so its motor frequently starts against a heavy load.
Correct answer: heavy- A. Cascade controlled A.C. motor
- B. Slip ring induction motor
- C. Three phase shunt wound com-mutator motor
- D. Any of the above
Explanation: Kiln drives require high starting torque and controlled speed, which can be obtained with cascade-controlled AC motors, slip-ring…
Correct answer: Any of the above- A. Synchronous motor
- B. Ship ring induction motor
- C. Squirrel cage induction motor
- D. D.C. shunt motor
Explanation: A DC shunt motor provides a broad speed-control range through field or armature-voltage control while maintaining nearly constant torque.
Correct answer: D.C. shunt motor- A. ball or roller
- B. needle
- C. bush
- D. thrust
Explanation: Motor rotors are commonly supported by ball or roller bearings because these bearings carry radial loads with low friction.
Correct answer: ball or roller- A. 'crowd' motion
- B. angle of swing
- C. cubic metres
- D. travel in metres
Explanation: An excavator’s size is generally specified by its bucket capacity, expressed in cubic metres.
Correct answer: cubic metres- A. Star-delta
- B. Resistance starting
- C. Auto-transformer
- D. None of the above
Explanation: Star-delta starting requires access to all six ends of the three stator windings so they can first be connected in star and then in delta.
Correct answer: Star-delta- A. Pulley
- B. Starter
- C. Foundation pedal
- D. Bearings
Explanation: A starter is essential because it limits starting current and provides switching and protection for the motor.
Correct answer: Starter- A. variable torque motor
- B. low torque variable speed motor
- C. self starting type synchronous motor
- D. low noise, slow speed motor
Explanation: A reluctance motor has a salient rotor and operates as a synchronous motor; in its commonly used polyphase form, it can start as an…
Correct answer: self starting type synchronous motor- A. is provided with slip rings
- B. requires starting gear
- C. has high cost
- D. is compact
Explanation: A reluctance motor has a simple rotor without windings, slip rings, or permanent magnets, so it is compact and mechanically robust.
Correct answer: is compact- A. Synchronous motor
- B. Reluctance motor
- C. Series motor
- D. Shunt motor
Explanation: Reluctance motors are suitable for textile and synthetic-fibre mills because they provide nearly constant-speed operation with a simple…
Correct answer: Reluctance motor- A. Induction motor
- B. Synchronous motor
- C. Capacitor start single phase motor
- D. Any of the above
Explanation: Induction motors are commonly used for elevators because they are rugged and provide suitable starting and speed characteristics…
Correct answer: Induction motor- A. Synchronous motor
- B. Schrage motor
- C. Induction motor
- D. Universal motor
Explanation: A synchronous motor runs at synchronous speed, which is fixed by supply frequency and the number of poles, so its speed remains…
Correct answer: Synchronous motor- A. Flux
- B. Armature current
- C. Flux and armature current
- D. Speed
Explanation: The DC motor torque relation is T ∝ ΦIa, so starting torque depends on flux and armature current.
Correct answer: Speed- A. Paper mills
- B. Grinding mills
- C. Air-conditioners
- D. Lifts and hoists
Explanation: Lifts and hoists repeatedly start, stop, and reverse while handling changing loads, so their motors must tolerate frequent switching and…
Correct answer: Lifts and hoists- A. Single phase motors
- B. Squirrel cage induction motors
- C. Slip ring induction motors
- D. D.C. motors
Explanation: DC motors are traditionally preferred for rolling mills because they provide high starting torque, smooth wide-range speed control, and…
Correct answer: D.C. motors- A. High efficiency operation
- B. Reversibility
- C. Variable speed drive
- D. High starting torque
Explanation: DC motors remain especially useful where a wide and precise range of speed control is required, because their speed can be controlled…
Correct answer: Variable speed drive- A. Inner race
- B. Outer race
- C. Cage
- D. Bush
Explanation: A ball bearing contains inner and outer races, rolling balls, and a cage that keeps the balls separated.
Correct answer: Bush- A. less than running torque
- B. same as running torque
- C. slightly more than running torque
- D. double the running torque
Explanation: A centrifugal pump develops torque approximately proportional to the square of speed, so its torque demand is very small at starting and…
Correct answer: less than running torque- A. Frame
- B. Rearing
- C. Stator winding
- D. Rotor winding
Explanation: The bearing, apparently misspelled as “Rearing,” needs maximum maintenance attention because it is subject to friction, lubrication…
Correct answer: Rearing- A. Starting characteristics
- B. Operating speed
- C. Horse power
- D. Speed control
Explanation: A centrifugal pump normally operates near a fixed speed, so speed control is usually not important in motor selection.
Correct answer: Speed control