1. The d.c. series motor should always be started with
load because
(A) at no load, it will rotate at
dangerously high speed.
(B) it will fail to start.
(C) it will not develop high starting
torque.
(D) all are true.
Ans: A
2. In a d.c. machine, the armature m.m.f.
is
(A) stationary w.r.t. armature.
(B) rotating w.r.t. field.
(C) stationary w.r.t. field.
(D) rotating w.r.t. brushes.
Ans: C
3. The current from the stator of an alternator is taken
out to the external load circuit through
(A) slip rings.
(B) commutator segments.
(C) solid connections.
(D) carbon brushes.
Ans: C
4. The most suitable servomotor for low power applications
is
(A) a dc series motor.
(B) a dc shunt motor.
(C) an ac two-phase induction motor.
(D) an ac series motor.
Ans: B
5. The torque, in a _____________is proportional to the
square of the armature current
(A) DC shunt motor
(B) stepper motor
(C) 2-phase servomotor
(D) DC series motor
Ans: D
6. A commutator in a d.c. machine
(A) Reduces power loss in armature.
(B) Reduces power loss in field circuit.
(C) Converts the induced a.c armature
voltage into direct voltage.
(D) Is not necessary.
Ans: C
7. A d.c. shunt motor runs at no load speed of 1140 r.p.m.
At full load, armature reaction weakens the main flux by 5% whereas the
armature circuit voltage drops by 10%. The motor full load speed in r.p.m. is
(A) 1080
(B) 1203
(C) 1000
(D) 1200
Ans: A
8. In DC generators, armature reaction is produced actually
by
(A) Its field current.
(B) Armature conductors.
(C) Field pole winding.
(D) Load current in armature.
Ans: D
9. As compared to shunt and compound DC
motors, the series DC motor will have the highest torque because of its
comparatively ____________ at the start.
(A) Lower armature resistance.
(B) Stronger series field.
(C) Fewer series turns.
(D) Larger armature current.
Ans: D
10. Application of DC motors is generally restricted to a few
load speed applications because of_____.
(A)
Cost of the motor is high
(B)
Problems with
mechanical commutation
(C)
Maintenance problems
(D)
None of the above
Ans: B
11. Which of the following could be lamina-proximately the
thickness of lamina proximation of a D.C. machine ?
(A) 0.005 mm
(B) 0.05 mm
(C) 0.5 m
(D) 5 m
Ans: C
12. The armature of D.C. generator is laminated to
(A) reduce the bulk
(B) provide the bulk
(C) insulate the core
(D) reduce eddy current loss
Ans: D
13. 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
14. The field coils of D.C. generator are usually made of
(A) mica
(B) copper
(C) cast iron
(D) carbon
Ans: B
15. The commutator segments are connected to the armature
conductors by means of
(A) copper lugs
(B) resistance wires
(C) insulation pads
(D) brazing
Ans: A