All Free Electrical Engineering MCQs with Answers

• A. silicon steel
• B. copper
• C. non-ferrous material
• D. cast-iron

Explanation: Silicon steel is used because its high magnetic permeability provides an efficient flux path, while laminations reduce eddy-current loss…

• A. rotor
• B. stator
• C. field
• D. armature

Explanation: The armature is the part containing conductors in which the useful e.m.f. is induced, whether it is the rotor or stator.

• A. E/2
• B. 2E
• C. slightly less than E
• D. E

Explanation: Generated e.m.f. follows E ∝ ΦN. With pole flux Φ constant, doubling speed N doubles the e.m.f., changing E to 2E.

• A. rectifier
• B. primemover
• C. rotating amplifier
• D. power pump

Explanation: A D.C. generator is called a rotating amplifier because a relatively small change in field power can control a much larger armature…

• A. Graphite brushes
• B. Carbon brushes
• C. Metal graphite brushes
• D. None of the above

Explanation: Metal-graphite brushes have a lower contact resistance and hence a smaller brush voltage drop than ordinary carbon or graphite brushes.

• A. number of pole pairs
• B. number of poles
• C. number of parallel paths
• D. number of commutator segments

Explanation: In a simplex lap winding, equalizer connections are made between points of equal potential, with one tapping arrangement for each pair of…

• A. high voltage, high current
• B. low voltage, high current
• C. high voltage, low current
• D. low voltage, low current

Explanation: A lap winding has as many parallel paths as poles, so it can carry high current at relatively low voltage.

• A. abrasion from dust
• B. excessive spring pressure
• C. rough commutator bars
• D. high mica insulation between com-mutation bars
• E. all of the above factors

Explanation: Brush wear can result from abrasive dust, excessive spring pressure, a rough commutator, or mica projecting above the copper bars.

• A. Dummy coils
• B. Commutator
• C. Eye bolt
• D. Equilizer rings

Explanation: The commutator mechanically rectifies the alternating emf induced in the armature conductors, delivering unidirectional current at the…

• A. mainly to reduce the eddy currents by providing local short-circuits
• B. to provide path for the circulation of cooling air
• C. to neutralise the cross-magnetising effect of the armature reaction
• D. none of the above

Explanation: Compensating windings are placed in the pole faces and carry armature current, producing an opposing mmf that neutralizes the…

• A. Insulation failure between two commutator bars
• B. Insulation failure between two turns of a coil
• C. Two of more turns of the same coil getting grounded
• D. All of the above

Explanation: A short circuit can result from insulation failure between commutator bars, between turns of a coil, or from turns of the same coil…

• A. speed of armature
• B. type of winding
• C. voltage
• D. amount of current to be collected

Explanation: The number of brushes is selected mainly according to the armature current that must be collected, since multiple brushes reduce current…

• A. electromagnets
• B. permanent magnets
• C. both A. and B.
• D. none of the above

Explanation: In the conventional DC generator, the magnetic field is produced by field-winding electromagnets, whose excitation can be separately…

• A. the brushes of opposite polarity should track each other
• B. the brushes of same polarity should track each other
• C. brush position has no effect on the commutator grooving
• D. None

Explanation: Brushes of opposite polarity are arranged to track the same commutator path, so their combined action helps prevent uneven wear and groove…

• A. reduces generator e.m.f.
• B. increases armature speed
• C. reduces interpoles flux density
• D. results in sparking trouble

Explanation: The demagnetizing component of armature reaction weakens the main field flux, so the generated emf decreases according to E ∝ ΦN.

• A. cumulatively compounded long shunt
• B. deferentially compounded long shunt
• C. cumulatively compounded short shunt
• D. differentially compounded short shunt

Explanation: When a compound generator operates as a motor, the armature current reverses relative to the series-field connection, reversing the…

• A. along neutral axis
• B. along field axis
• C. in any of the above positions
• D. in none of the above positions

Explanation: A coil is short-circuited by the brush while it is passing through the magnetic neutral axis, which is the commutation zone.

• A. lap winding
• B. wave moving
• C. duplex winding
• D. any of the above

Explanation: A DC welding generator requires high current at relatively low voltage, which is provided by a lap winding.

• A. brushes
• B. field
• C. armature
• D. load

Explanation: Critical resistance is the maximum field-circuit resistance at which a shunt generator can just build up its voltage.

• A. 640 V
• B. 620 V
• C. 600 V
• D. 580 V

Explanation: For a generator, terminal voltage is approximately E minus the armature voltage drop: 600 − (200 × 0.1) = 580 V. The correct option is d.