Single Phase Motor Questions Answers

1. Which of the following motors can be used for unity power factor ?

(a) Capacitor run motor
(b) Shaded pole motor
(c) Hysteresis motor
(d) Schrage motor

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2. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of

(a) high inductance of field and armature circuits
(b) induced current in rotor due to variations of flux
(c) fine copper wire winding
(d) none of the above

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3. The direction of rotation of universal motor can reversed the by reversing the flow of current through

(a) armature winding
(b) field winding
(c) either armature winding or field winding
(d) none of the above

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4. Which motor is normally free from mechanical and magnetic vibrations?

(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor

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5. A reluctance motor

(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above

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6. In a hysteresis motor, the rotor must have

(a) retentivity
(b) resistivity
(c) susceptibility
(d) none of the above

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7. The rotor of a hysteresis motor is made of

(a) aluminium
(b) cast iron
(c) chrome steel
(d) copper

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8. Which of the following applications always have some load whenever switched on ?

(a) Vacuum cleaners
(b) Fan motors
(c) Pistol drills
(d) All of the above

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9. In repulsion motor, maximum torque is developed when

(a) brush axis is at 45 degrees electrical to the field axis
(b) brush axis coincides with the field axis
(c) brush axis is at 90 degrees electrical to the field axis
(d) none of the above

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10. If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

(a) damage to the starting winding
(b) damage to the centrifugal switch
(c) over-loading of running winding
(d) none of the above

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11. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.

(a) shunt motor
(b) series motor
(c) compound motor
(d) separately excited motor

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12. In a ceiling fan employing capacitor run motor

(a) secondary winding surrounds the primary winding
(b) primary winding surrounds the secondary winding
(c) both are usual arrangements
(d) none of the above

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13. The shaded pole motor is used for

(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque

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14. The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it

(a) improves the efficiency
(b) helps the rotor teeth to remain under the stator teeth
(c) helps in reducing the tendency of the rotor teeth to remain under the stator teeth
(d) improves the power factor

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15. The speed/load characteristics of a universal motor is same as that of

(a) A.C. motor
(b) D.C. shunt motor
(c) D.C. series motor
(d) none of the above

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16. The motor used for the compressors is

(a) D.C. series motor
(b) shaded pole motor
(c) capacitor start capacitor run motor
(d) reluctance motor

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17. In repulsion motor, zero torque is developed when

(a) brush axis is 45 degrees electrical to field axis
(b) brush axis coincides with the field axis
(c) brush axis is 90 degrees electrical to field axis
(d) either brush axis coincides with the field axis or brush axis is 90 degrees electrical to field axis

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18. Centrifugal switch disconnects the auxiliary winding of the motor at about……………. percent of synchronous speed.

(a) 30 to 40
(b) 70 to 80
(c) 80 to 90
(d) 100

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19. Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a

(a) magnetic relay
(b) thermal relay
(c) centrifugal switch
(d) none of the above

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20. If a single phase induction motor runs slower than normal, the most likely defect is

(a) worn bearings
(b) short-circuit in the winding
(c) open-circuit in the winding
(d) none of the above

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