100 TOP Objective D.C Motors Questions and Answers pdf

101.    Which of the following loss in a D.C. generator is dissipated in the form of heat?
(a)    Mechanical loss
(b)    Core loss
(c)    Copper loss     
(d)     All of the above
Ans: d

102.    Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
(a) Hysteresis losses
(b) Eddy current losses
(c) Copper losses
(d) Windage losses
Ans: b

103.    The total losses in a well designed D.C. generator of 10 kW will be nearly
(a) 100 W 
(b) 500 W
(c) 1000 W 
(d) 1500 W
Ans: b

104.    The condition for maximum efficiency for a D.C. generator is
(a)    eddy current losses = stray losses
(b)    hysteresis losses = eddy current losses
(c)    copper losses = 0
(d)    variable losses = constant losses
Ans: d

105.    D.C. generators are normally designed for maximum efficiency around
(a) full-load 
(b) rated r.p.m.
(c) rated voltage  
(d) all of the above
Ans: a

106.    In a D.C. generator, the iron losses mainly take place in
(a)     yoke 
(b)     commutator
(c)    armature conductors
(d)    armature rotor
Ans: d

107.    D.C. generators are installed near the load centres to reduce
(a) iron losses 
(b) line losses
(c) sparking 
(d) corona losses
Ans: b

108.    The purpose of retardation test on D.C. shunt machines is to find out
(a)    stray losses
(b)    eddy current losses
(c)    field copper losses
(d)     windage losses
Ans: a

109.    Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
(a)    Swinburne's test
(b)    Hopkinson's test
(c)    Field test 
(d)     Brake test
Ans: c

110.    Hopkinson's test on D.C. machines is conducted at
(a) no-load 
(b) part load
(c) full-load 
(d) overload

Ans: c