MULTIPLE CHOICE QUESTIONS
Q.1 The number of stator poles produced in the rotating magnetic field of a 3-phase induction motor having 3 slots per pole per phase is
(A) 3
(B) 6
(C) 2
(D) 12
Q.2 The power factor of a squirrel-cage induction motor is
(A) low at light loads only
(B) low at heavy loads only
(C) low at light and heavy loads both
(D) low at rated load only.
Q.3 Which of the following rotor quantity in a SCIM does NOT depend on its slip ?
(A) reactance
(B) speed
(C) induced emf
(D) frequency.
Q.4 A 6-pole, 50-Hz, 3-phase induction motor is running at 950 rpm and has rotor Cu loss of
5 kW. Its rotor input is ......kW.
(A) 100
(B) 10
(C) 95
(D) 5.3.
Q.5 The efficiency of a 3-phase induction motor is approximately proportional to
(A) (1. s)
(B) s
(C) N
(D) Ns.
Q.6 A 6-pole, 50-Hz, 3-phase induction motor has a full load speed of 950 rpm. At half-load, its speed would be ......rpm.
(A) 475
(B) 500
(C) 975
(D) 1000
Q.7 If rotor input of a SCIM running with a slip of 10% is 100 kW, gross power developed by its rotor is ...... kW.
(A) 10
(B) 90
(C) 99
(D) 80
Q.8 Pull-out torque of a SCIM occurs at that value of slip where rotor power factor equals
(A) unity
(B) 0.707
(C) 0.866
(D) 0.5
Q.9 When load is placed on a 3-phase induction motor, its
(A) rotor induced emf
(B) rotor current
(C) rotor torque
(D) applied torque.
Q.10 When applied rated voltage per phase is reduced by one-half, the starting torque of a SCIM becomes ...... of the starting torque with full voltage.
(A) 1/2
(B) 1/4
(C) 1/ 2
(D) 3/2
