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. Power density
- B. Temperature difference between heated surface and coolant
- C. Thermal resistivity, density, specific heat
- D. Gravitational constant
- E. All of the above
Explanation: Convective heat transfer is influenced by the temperature difference and by fluid properties such as density, specific heat and thermal…
Correct answer: All of the above- A. Copper
- B. Aluminium
- C. Steel
- D. Cast-iron
Explanation: Cast iron is used for starter resistance grids because its relatively high resistivity allows compact resistance and its high heat…
Correct answer: Cast-iron- A. conduction
- B. convection
- C. radiation
- D. any of the above
Explanation: Radiation depends strongly on the surface temperature and emissivity, which is affected by colour, roughness and surface finish.
Correct answer: radiation- A. Grey cast-iron
- B. Cast steel
- C. High carbon steel
- D. Stainless steel
Explanation: Cast steel is selected for magnetic-circuit sections carrying steady flux when high mechanical strength is important.
Correct answer: Cast steel- A. zero
- B. low
- C. high
- D. none of the above
Explanation: Hot-rolled magnetic sheets have relatively low permeability compared with specially processed cold-rolled grain-oriented sheets.
Correct answer: low- A. Silver
- B. Steel
- C. Aluminium
- D. Copper
Explanation: Copper is used most widely for machine windings because it combines high electrical conductivity with ductility, allowing it to be drawn…
Correct answer: Copper- A. Cast steel
- B. Aluminium
- C. Soft steel
- D. Cast iron
Explanation: Cast iron has comparatively low permeability, but it is inexpensive and mechanically strong; its greater weight is acceptable when cost…
Correct answer: Cast iron- A. The flux is constant with respect to time and is stationary and the coil moves through it
- B. The coil is stationary with respect to flux and the flux varies in magnitude with respect to time
- C. Both the changes mentioned above occur together, i.e., the coil moves through a time varying field
- D. All of the above
Explanation: Flux linkages change either when a stationary coil moves through a magnetic field, when the flux varies around a stationary coil, or when…
Correct answer: All of the above- A. Induction
- B. Interaction
- C. Alignment
- D. All of the above
Explanation: Electromagnetic machines involve induction for generating e.m.f., interaction between magnetic fields for producing force or torque, and…
Correct answer: All of the above- A. d.c. series motor .
- B. d.c. shunt motor
- C. induction motor
- D. synchronous motor
Explanation: The induction motor air gap is kept carefully controlled because it strongly affects magnetizing current and hence the power factor.
Correct answer: induction motor- A. low
- B. medium
- C. high
- D. any of the above
Explanation: Mechanical design becomes especially critical at high speed because centrifugal forces, vibration, bearing stress, and rotor unbalance…
Correct answer: high- A. Saturation
- B. Temperature rise
- C. Efficiency
- D. Power factor
- E. All above
Explanation: Saturation, excessive temperature rise, low efficiency, and poor power factor all restrict the practical design of an electrical machine.
Correct answer: All above- A. drastically increased
- B. drastically reduced
- C. unaffected
- D. none of the above
Explanation: Insulation deteriorates rapidly when its temperature exceeds the permissible limit, reducing its dielectric strength and service life.
Correct answer: drastically reduced- A. small size
- B. medium size
- C. large size
- D. any of the above
Explanation: Machines rated up to roughly 750 W are conventionally grouped as small-size machines.
Correct answer: small size- A. low power factor
- B. high power factor
- C. high over load capacity
- D. any of the above
Explanation: A small air gap reduces the reluctance of the magnetic circuit and therefore lowers the magnetizing current.
Correct answer: high power factor216. The efficiency of a machine should be as ____________ as possible to reduce the operating cost?
- A. high
- B. low
- C. either of the above
- D. none of the above
Explanation: Higher efficiency means less input power is wasted as heat and losses for the same useful output.
Correct answer: high- A. small size machines
- B. medium size machines
- C. large size machines
- D. any of the above
Explanation: Machines rated from a few kilowatts to approximately 250 kW are generally classified as medium-size machines.
Correct answer: medium size machines- A. small
- B. medium
- C. large
- D. any of the above.
Explanation: In large machines, the shaft is relatively long and flexible, so its deflection and critical speed become important design considerations.
Correct answer: large- A. Diamond
- B. High speed steel
- C. Mild steel
- D. Cast iron
Explanation: Cast iron has strong internal friction and a relatively non-elastic structure, allowing it to absorb vibrational energy effectively.
Correct answer: Cast iron220. Copper, even though costly, finds use in the windings of electrical machines because_____________?
- A. copper points offer low contact resistance
- B. copper can be easily soldered and welded
- C. copper windings are less bulky and the machines become compact
- D. all of the above
Explanation: Copper combines very high conductivity with good solderability and weldability, while its low resistivity permits smaller, less bulky…
Correct answer: all of the above