DC MOTOR MCQS SET 08

DC MOTOR MCQS SET 08

1. If I2 be the armature current, then speed of a D.C. shunt motor is
(a) Independent of Ia
(b) Proportional to la
(c) Varies as (Ia)
(d) varies as la 

Ans:  a
2. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
(a) Remain unchanged
(6) Reduce to one-fourth value
(c) Increase four folds
(d) Be doubled 

Ans:  a

3. At the instant of starting when a D.C. motor is put on supply, it behaves like
(a) a highly resistive circuit
(6) a low resistance circuit
(c) a capacitive circuit
(d) None of the above 

Ans:  b

4. The speed of a D.C. motor can be varied by varying
(a) Field current
(b) Applied voltage
(c) Resistance in series with armature
(d) Any of the above 

Ans:  d

5. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
(a) Low cost
(b) Wide speed range
(c) Stability
(d) High starting torque. 

Ans:  a

6. For a D.C. shunt motor if the excitation is changed
(a) torque will remain constant
(b) torque will change but power will remain constant
(c) torque and power both will change
(d) torque, power and speed, all will change 

Ans:  b

7. Which motor has the poorest speed control?
(a) Differentially compounded motor
(b) Cumulatively compounded motor
(c) Shunt motor
(d) Series motor 

Ans:  d

8. The plugging gives the
(a) zero torque braking
(b) smallest torque braking
(c) highest torque braking
(d) none of the above 

Ans:  c

9. The armature voltage control of D.C. motor provides
(a) constant voltage drive
(b) constant current drive
(c) constant torque drive
(d) none of the above 

Ans:  c

10. If 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
(6) 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 recom-mended by manufacturer and select the next higher H.P. motor
Ans:  d