Electrical Engineering Mid - II, November - 2014

1.The value of back emf is maximum at
  • No load
  • Full load
  • half full load
  • none
Answer: A
2.The field winding of a self-excited dc motor is excited by a
  • dc
  • ac
  • either A or B
  • its own current
Answer: D
3.When the speed of the dc motor increases its armature current
  • Increases
  • decreases
  • remains constant
  • none
Answer: B
4.A step up transformer increases
  • Power
  • current
  • voltage
  • frequency
Answer: C
5.Which of the following does not change in transformer
  • current
  • Voltage
  • frequency
  • all the above
Answer: C
6.A wound rotor is mainly used in applications where
  • high starting torque is required
  • speed control is required
  • less costly motor is required
  • high rotor resistance is required
Answer: A
7.In a 3 - phase induction motor, the rotor speed is ________ the synchronous speed
  • Greater than
  • smaller than
  • equal to
  • none of the above
Answer: B
8.The conditions of induction motor at standstill resemble those of a transformer whose secondary is
  • Open circuited
  • short circuited
  • supplying a variable resistive load
  • none of the above
Answer: A
9.The non - salient pole construction is used for __________ alternator
  • Low speed
  • medium speed
  • high speed
  • none
Answer: C
10.AC generators are rated in ___________
  • H.P
  • kVAR
  • MW
  • MVA or KVA
Answer: D
11.The armature current and field current are equal in the case of ____________ machines
Answer: DC series motor
12.The terminal voltage equation for the motor is ___________
Answer: Vt = Eb + Ia Ra
13.A 3 point starter is suitable for _____________ motors
Answer: DC shunt motor
14.If a 4 pole induction motor as a synchronous speed of 1500 rpm then supply frequency is _________
Answer: 50 HZ
15.In a 3-phase system, each phase separates by __ degrees with respect to other phases
Answer: 120
16.The rotor of an alternator has __________slip rings for DC supply.
Answer: 2
17.In the short circuit test do transformer, we generally short circuit __________ winding
Answer: Low voltage
18.The relation among the synchronous speed (NS ), rotor speed (N) and slip (s) is
Answer: N = (1 - S) Ns
19.If the supply voltage of a 3-Phase induction Motor is increased , then torque is __________
Answer: Increases
20.Open circuit test of the transformer gives _____________ losses
Answer: Iron losses