51. In an induction motor if the flux density is reduced to one–half of its normal value then the torque will
- Reduce to one half
- Reduce to one fourth
- Remain unchanged
- Increase four times
52. The torque developed in an induction motor is nearly proportional to
- 1/V
- V
- V2
- None of these
53. The starting torque of a squirrel cage induction motor is
- very large
- very low
- slightly more than full-load torque
- zero
54. When the applied voltage per phase is reduced to one-half. The starting torque of a three-phase squirrel cage induction motor becomes
- 1/2 of the initial value
- 1/4 of the initial value
- Twice of the initial value
- 4 times of the initial value
55. In a 3-phase induction motor, the maximum torque
- is independent of rotor circuit resistance
- varies as rotor resistance
- varies as the square of rotor resistance
- varies inversely as rotor circuit resistance
56. For a slip-ring induction motor, if the rotor resistance is increased, then
- starting torque and efficiency increase
- starting torque decreases but efficiency increases
- starting torque increases but efficiency decreases
- starting torque and efficiency decrease
57. An induction motor has a rotor resistance of 0.002 ohm/phase. If the resistance is increased to 0.004 ohm/phase then the maximum torque will
- reduce to half
- increase by 100%
- increase by 200%
- remain unaltered
58. Break down torque of a three-phase induction motor of negligible stator impedance is
- directly proportional to the rotor resistance
- inversely proportional to the rotor resistance
- directly proportional to the reactance
- inversely proportional to the rotor leakage reactance
59. In three phase induction motor, the torque developed is maximum when the rotor circuit resistance per phase is equal to
- rotor leakage reactance per phase at standstill
- slip times the rotor leakage reactance per phase at standstill
- stator resistance per phase
- stator leakage reactance per phase
60. A 4-pole, 50Hz, 3-phase induction motor has blocked rotor reactance per phase which is four times the rotor resistance per phase. The speed at which maximum torque developed is
- 1,125 rpm
- 1,500 rpm
- 1,050 rpm
- 1,210 rpm