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Electrical Engineering Objective Questions { DC Motors }

225. 1f a D.C. motor designed for 40?C ambient temperature is to be used for 50?C ambient temperature, then the motor
A. of lower H.P. should be selected
B. of higher H.P. should be selected
C. can be used for 50?C ambient temperature also
D. is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor
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226.  If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
A. regenerative
B. plugging
C. dynamic braking
D. none of the above
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227.  Which of the following motors one will choose to drive the rotary compressor?
A. D.C. shunt motor
B. D.C. series motor
C. Universal motor
D. Synchronous motor
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228.  If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
A. increase
B. decrease
C. remain sa me
D. become zero
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229.  Why are the D.C. motors preferred for traction applications?
A. Torque and speed are inversely proportional to armature current
B. Torque is proportional to armature current
C. Torque is proportional to square root of armature current
D. The speed is inversely proportional to the torque and the torque is proportional to square of armature current
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230.  Which of the following motors have almost constant speed over their full load range?
A. A.C. series motors
B. D.C. shunt motors
C. Low resistance squirrel cage motors
D. Both (c) and (b)
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231.  Which of the following motors in usually used in house-hold refrigerators?
A. D.C. shunt motor
B. D.C. series motor
C. Single phase induction motor
D. Reluctance motor
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