Electrical Machines Objective Test No. 15


     MULTIPLE CHOICE QUESTIONS


Q.1 In a d.c. motor, unidirectional torque is produced with the help of
 (A) brushes
 (B) commutator
 (C) end-plates
 (D) both (a) and (b)

Q.2 The counter e.m.f. of a d.c. motor
 (A) often exceeds the supply voltage
 (B) aids the applied voltage
 (C) helps in energy conversion
 (D) regulates its armature voltage

Q.3 The normal value of the armature resistance of a d.c. motor is
 (A) 0.005
 (B) 0.5
 (C) 10
 (D) 100

Q.4 The Eb/V ratio of a d.c. motor is an indication of its
 (A) efficiency
 (B) speed regulation
 (C) starting torque
 (D) Running Torque

Q.5 The mechanical power developed by the armature of a d.c. motor is equal to
 (A) armature current multiplied by back e.m.f.
 (B) power input minus losses
 (C) power output multiplied by efficiency
 (D) power output plus iron losses

Q.6 The induced e.m.f. in the armature conductors of a d.c. motor is
 (A) sinusoidal
 (B) trapezoidal
 (C) rectangular
 (D) alternating

Q.7 A d.c. motor can be looked upon as d.c. generator with the power flow
 (A) reduced
 (B) reversed
 (C) increased
 (D) modified

Q.8 In a d.c. motor, the mechanical output power actually comes from
 (A) field system
 (B) air-gap flux
 (C) back e.m.f.
 (D) electrical input power

Q.9 The maximum torque of d.c. motors is limited by
 (A) commutation
 (B) heating
 (C) speed
 (D) armature current

Q.10 Which of the following quantity maintains the same direction whether a d.c. machine runs as a generator or as a motor ?
 (A) induced e.m.f.
 (B) armature current
 (C) field current
 (D) supply current