Sunday, October 28, 2012

DC Motors: Part-10 Objective Questions

Solved Objective Questions from DC Machines:

[1] Voltage equation of a dc motor is
A.  V = Eb + IaRa
B.  Eb = V  + IaRa
C.  V = Eb/IaRa
D.  V = Eb + Ia2Ra
E.   None of the above

[2] Both Hopkinson's test and Field test 
A.   Require two electrically coupled series motors
B.   Need two similar mechanically coupled motors
C.   Use negligible power
D.   Are regenerative tests
E.    None of the above

[3] which of the following motor has the constant speed?
A.    Series motor
B.    Shunt motor
C.    Cumulatively compound motor
D.    All of the above
E.    None of the above

[4] The usual test to find the efficiency of the traction motor is
A.  Field's test
B.  Retardation test
C.  Hopkinson's test
D.  Swinburn's test
E.   None of the above

[5] A DC series motor is best for driving
A.   Lathes
B.   Cranes and hoists
C.   Shears and punches
D.   Machine tools
E.   None of the above

[6] Retardation test on a dc shunt motor is used for finding 
A.   Stray loss
B.   Copper loss
C.   Friction loss
D.   Iron loss
E.   None of the above

[7] In a DC series motor increasing the load current will
A. Decrease the speed
B. Increase the speed
C. Better commutation
D. Increase the back emf
E. None of the above

[8] One of the main advantage of the swinburn's test is
A. It is applicable both shunt and compound motors
B. It needs one running test
C. It is very economical and convenient
D. It ignores any charge in iron loss
E. None of the above

[9] the main disadvantage of hopkinson's test for finding efficiency of shunt dc motors is that it
A. Requires full load power
B. Ignores any change in iron loss
C. Needs one motor and one generator
D. Requires two identical shunt machines
E. None of the above

[10] The most economical method of finding no losses of a large dc shunt motor is
A. Hopkinson's test
B. Swinburn's test
C. Retardation test
D. Field's test
E. None of the above


5:23 AM

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