Electrical Engineering Question Answers- Jan 2018

Q.#1. The resistance of armature winding depends on
(a) length of conductor
(b) cross-sectional area of the conductor
(c) number of conductors
(d) all of the above
Ans: (d) all of the above

Q.#2. A commutator in a d.c. machine
 (A) Converts the induced a.c armature voltage into direct voltage.
 (B) Reduces power loss in field circuit.
 (C) Reduces power loss in armature.
 (D) Is not necessary.
Ans:  (A) Converts the induced a.c armature voltage into direct voltage.

Q.#3. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) any of the above
(c) imperfect contact
(d) rough commutator surface
Ans: (b) any of the above


Q.#4. The introduction of interpoles in between the main pole improves the performance of
d.c. machines, because
(A) A counter e.m.f. is induced in the coil undergoing commutation.
(B) The flux waveform is improved with reduction in harmonics.
(C) The inequality of air flux on the top and bottom halves of armature is removed.
(D) The interpole produces additional flux to augment the developed torque.
Ans: (A) A counter e.m.f. is induced in the coil undergoing commutation.

Q.#5. A differentiator is usually not a part of a control system because it
(a) increases input noise
(b) reduces the gain margin
(c) reduces damping
(d) increases error
Ans: (a) increases input noise

Q.#6. In D.C. generators, the brushes on commutator remain in contact with conductors
which
(a) lie under interpolar region
(b) lie under north pole
(c) lie under south pole
(d) are farthest from the poles
Ans: (a) lie under interpolar region

Q.#7. In induction motor, percentage slip depends on
(a) supply frequency
(b) copper losses in motor
(c) supply voltage
(d) none of the above
Ans:  (b) copper losses in motor

Q.#8. A 1:5 step-up transformer has 120V across the primary and 600 ohms resistance
across the secondary. Assuming 100% efficiency, the primary current equals
(A) 0.2 Amp.
(B) 5 Amps.
(C) 10 Amps.
(D) 20 Amps.
Ans: (A) 0.2 Amp.


Q.#9. Less maintenance troubles are experienced in case of
(a) slip ring induction motor
(b) squirrel cage induction motor
(c) both (a) and (b)
(d) none of the above
Ans: (b) squirrel cage induction motor

Q.#10. The spring material used in a spring control device should have the following property.
(a) Should be non-magnetic
(b) Most be of low temperature co-efficient
(c) Should have low specific resistance
(d) Should not be subjected to fatigue
(e) All of the above
Ans: (e) All of the above

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