Q.1
Lubricant used for ball bearing is usually
  • graphite
  • grease
  • mineral oil
  • molasses
Q.2
A squirrel cage induction motor is not selected when
  • initial cost is the main consideration
  • maintenance cost is to be kept low
  • higher starting torque is the main consideration
  • all above considerations are involved
Q.3
Less maintenance troubles are experienced in case of
  • slip ring induction motor
  • squirrel cage induction motor
  • both (a) and (b)
  • none of the above
Q.4
In a squirrel cage motor the induced e.m.f. is
  • dependent on the shaft loading
  • dependent on the number of slots
  • slip times the stand still m.f. induced in the rotor
  • none of the above
Q.5
The purpose of using short-circuit gear is
  • to short circuit the rotor at slip rings
  • to short circuit the starting resis¬tances in the starter
  • to short circuit the stator phase of motor to form star
  • none of the above
Q.6
For driving high inertia loods best type of induction motor suggested is
  • slip ring type
  • squirrel cage type
  • any of the above
  • none of the above
Q.7
Reduced voltage starter can be used with
  • slip ring motor only but not with squirrel cage induction motor
  • squirrel cage induction motor only but not with slip ring motor
  • squirrel cage as well as slip ring induction motor
  • none of the above
Q.8
An induction motor can run at synchronous speed when
  • it is run on load
  • it is run in reverse direction
  • it is run on voltage higher than the rated voltage
  • m.f. is injected in the rotor circuit
Q.9
The torque developed by a 3-phase induction motor least depends on
  • rotor current
  • rotor power factor
  • rotor m.f.
  • shaft diameter
Q.10
In an induction motor if air-gap is increased
  • the power factor will be low
  • windage losses will be more
  • bearing friction will reduce
  • copper loss will reduce In an induction motor
Q.11
Insertion of resistance in the rotcir of an induction motor to develop a given torque
  • decreases the rotor current
  • increases the rotor current
  • rotor current becomes zero
  • rotor current rernains same
Q.12
When /?2 is tne rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condi-tions will be
  • sR2X2 = 1
  • sR2 = X2
  • R2 = sX2 i
  • R2 = s2X2
Q.13
In case of a double cage induction motor, the inner cage has
  • high inductance arid low resistance
  • low inductance and high resistance
  • low inductance and low resistance
  • high inductance and high resis¬tance
Q.14
Insertion of reactance in the rotor circuit
  • reduces starting torque as well as maximum torque
  • increases starting torque as well as maximum torque
  • increases starting torque but maxi-mum torque remains unchanged
  • increases starting torque but maxi-mum torque decreases
Q.15
The torque of an induction motor is
  • directly proportional to slip
  • inversely proportional to slip
  • proportional to the square of the slip
  • none of the above
Q.16
In a star-delta starter of an induction motor
  • resistance is inserted in the stator
  • reduced voltage is applied to the stator
  • resistance is inserted in the rotor
  • applied voltage per1 stator phase is 57.7% of the line voltage
Q.17
Slip ring motor is preferred over squirrel cage induction motor where
  • high starting torque is required
  • load torque is heavy
  • heavy pull out torque is required
  • all of the above
Q.18
A pump induction motor is switched on to a supplylower than its rated voltage.The pump runs. What will eventually happen ? It will
  • stall after sometime
  • stall immediately
  • continue to run at lower speed without damage
  • get heated and subsequently get damaged
Q.19
AkW, 3-phase,volts,Hz, A.C. induction motor has a speed ofr.p.m. onfull load. The machine has 6 poles. The slip of the machine will be
  • 0.01
  • 0.02
  • 0.03
  • 0.04
Q.20
What will happen if the relative speed between the rotating flux of stator and rotor ofthe induction motor is zero ?
  • The slip of the motor will be 5%
  • The rotor will not run
  • The rotor will run at very high speed
  • The torque produced will be very large
0 h : 0 m : 1 s