Electrical machines: Part 2

Electrical machines: Part 2

[1] In a DC motor, unidirectional torque is produced with the help of
a. Brushes
b. Commutator
c. End-plates
d. Both a and b

Ans: D

[2] The counter emf of dc motor
a. Often exceeds the supply voltage
b. Aids the applied voltage
c. Helps in energy conversion
d. Regulates its armature voltage

Ans:C

[3] The Eb/V ratio of a dc motor is an indication of its
a. Efficiency
b. Speed regulation
c. Starting torque
d. Running Torque

Ans:A

[4] The induced emf in the armature conductors of a dc motor is
a. Sinusoidal
b. Trapezoidal
c. Rectangular
d. Alternating

Ans: A

[5] A dc motor can be looked upon as dc generator with the power flow
a. Reduced
b. Reversed
c. Increased
d. Modified

Ans:B

[6] A series motor is best suited for driving
a. Lathes
b. Cranes and hoists
c. Shears and punches
d. Machine tools

Ans: B

[7]The Ta/Ia graph of a dc series motor is a
a. Parabola from no load to overload
b. Straight line throughout
c. Parabola throughout
d. Parabola upto full load and a straight line at overloads

Ans: D

[8] When load is removed, .......motor will run at the highest speed.
a. Shunt
b. Cumulative - compound
c. Differential compound
d. Series

Ans: D

[9] The power factor of a squirrel cage induction motor is
a. Low at light loads only
b. Low at heavy loads only
c. Low at light and heavy loads both
d. Low at rated load only

Ans: A

[10] The synchronous speed of a linear induction motor does not depend on
a. Width of pole pitch
b. Number of poles
c. Supply frequency
d. Any of the above

Ans: B. See the comment for explanation..