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. wave wound
- B. lap wound
- C. delta wound
- D. duplex wound
Explanation: Equalizer rings are used with lap windings to equalize the voltages of parallel paths and prevent circulating currents caused by unequal…
Correct answer: lap wound- A. to avoid sudden loading of the primemover
- B. to avoid mechanicaljerk to the shaft
- C. to avoid burning of switch contacts
- D. all above
Explanation: A generator is connected to or removed from busbars under floating, or no-load, conditions to prevent sudden prime-mover loading, shaft…
Correct answer: all above- A. crossmagnetising
- B. demagnetising
- C. magnetising
- D. none of above
Explanation: For an unsaturated machine, the armature-reaction flux mainly acts at right angles to the main field and distorts it, so it is…
Correct answer: crossmagnetising- A. demagnetisation only
- B. cross magnetisation as well as mag¬netisation
- C. crossmagnetisation as well as demagnetising
- D. cross magnetisation only
Explanation: Moving the brushes away from the geometrical neutral axis tilts the armature-reaction axis, resolving it into both a cross-magnetising…
Correct answer: crossmagnetisation as well as demagnetising- A. lie under south pole
- B. lie under north pole
- C. lie under interpolar region
- D. are farthest from the poles
Explanation: Commutation occurs while a coil is short-circuited by a brush, and the corresponding conductors lie in the interpolar or neutral region…
Correct answer: lie under interpolar region- A. graphite
- B. paper
- C. mica
- D. insulating varnish
Explanation: Mica is used between commutator segments because it has high dielectric strength, good mechanical stability, and withstands the heat and…
Correct answer: mica- A. mica
- B. copper
- C. cast iron
- D. carbon
Explanation: Carbon is commonly used for DC-machine brushes because it provides suitable electrical contact while limiting commutator wear and reducing…
Correct answer: carbon- A. 4
- B. 8
- C. 16
- D. 32
Explanation: Sixteen coils in a two-layer winding provide 32 active conductors. Pole pitch is the number of conductors per pole, so it is 32 divided by…
Correct answer: 8- A. Blv
- B. Blv2
- C. Bl2v
- D. Bl2v2
Explanation: For a conductor of effective length l moving at velocity v through flux density B, the motional emf is e = Blv when the motion is…
Correct answer: Blv- A. imperfect brush contact
- B. field resistance less than the critical resistance
- C. no residual magnetism in the generator
- D. faulty shunt connections tending to reduce the residual magnetism
Explanation: A shunt generator builds up when its field resistance is below the critical resistance, so that option supports voltage build-up rather…
Correct answer: field resistance less than the critical resistance- A. carbon
- B. soft copper
- C. hard copper
- D. all of above
Explanation: Carbon or graphite brushes are the usual choice because they provide suitable conductivity while limiting commutator wear and sparking.
Correct answer: carbon792. In D.C. generators, current to the external circuit from armature is given through_____________?
- A. commutator
- B. solid connection
- C. slip rings
- D. none of above
Explanation: The armature generates alternating emf, and the commutator mechanically rectifies it so that current delivered to the external circuit is…
Correct answer: commutator- A. speed
- B. load
- C. voltage
- D. speed and voltage
Explanation: Iron losses are mainly set by flux density and frequency, which are approximately constant in a D.C.
Correct answer: load- A. reduce the bulk
- B. provide the bulk
- C. insulate the core
- D. reduce eddy current loss
Explanation: Laminating the armature core breaks up circulating paths for induced currents, greatly reducing eddy-current loss.
Correct answer: reduce eddy current loss- A. case iron
- B. carbon
- C. silicon steel
- D. stainless steel
Explanation: Armature-core laminations are made from silicon steel because its high electrical resistivity reduces eddy-current loss and its magnetic…
Correct answer: silicon steel- A. copper lugs
- B. resistance wires
- C. insulation pads
- D. brazing
Explanation: Commutator segments are joined to the armature coil ends using copper lugs, which provide a strong, low-resistance electrical connection.
Correct answer: copper lugs- A. length of conductor
- B. cross-sectional area of the conductor
- C. number of conductors
- D. all of the above
Explanation: From R = ρL/A, resistance increases with conductor length and decreases with cross-sectional area; the number of conductors affects the…
Correct answer: all of the above- A. mica
- B. copper
- C. cast iron
- D. carbon
Explanation: Field coils carry current and must produce the required magnetic field with low resistance, so they are normally wound from insulated…
Correct answer: copper- A. copper is harder than mica
- B. mica and copper are equally hard
- C. mica is harder than copper
- D. none of the above
Explanation: Mica is harder than copper, so it is used as insulation between commutator segments and must be undercut slightly below the copper surface…
Correct answer: mica is harder than copper- A. motion of conductor
- B. lines of force
- C. either of the above
- D. none of the above
Explanation: In Fleming’s right-hand rule, the thumb shows conductor motion, the forefinger shows magnetic-field or flux direction, and the middle…
Correct answer: lines of force