DC MOTOR
1. In a dc Motor, unidirectional torques is produced with the help of
a. Brushes
b. Commutator
c. End plates
d. Both a and b….
2. The counter emf of a dc motor
a. Often exceeds the supply voltage
b. Aids the applied voltage
c. Helps in energy conversion….
d. Regulates its armature voltage
3. The normal value of the armature resistance of a dc motor is
a. 0.005
b. 0.5 ….
c. 10
d. 100
4. The Eb/V ratio of dc motor is an indication of its
a. Efficiency…..
b. Speed regulation
c. Starting torque
d. Running torque
5. The mechanical power developed by the armature of a dc motor is equal to
a. Armature current multiplied by back emf….
b. Power input minus losses
c. Power output multiplied by efficiency
d. Power output plus iron losses
6. The induced emf in the armature conductors of a dc motor is
a. Sinusoidal….
b. Trapezoidal
c. Rectangular
d. Alternating
7. A dc motor can be looked upon as a dc generator with the power flow
a. Reduced
b. Reversed……
c. Increased
d. Modified
8. In a dc motor, the mechanical output power actually comes from
a. Field system
b. Air gap flux
c. Back emf
d. Electrical input power……
9. The maximum torque of dc motors is limited by
a. Commutation…….
b. Heating
c. Speed
d. Armature current
10. Which of the following quantity maintains the same direction whether a dc machine runs as a generator or as a motor?
a. Induced emf……
b. Armature current
c. Field current
d. Supply current
11. Under constant load conditions, the speed of a dc motor is affected by
a. Field flux…….
b. Armature current
c. Back emf
d. Both b and c
12. The current drawn by a 120 V dc motor of armature resistance 0.5 ohm and back emf 110V is ——- Ampere
a. 20…….
b. 240
c. 220
d. 5
13. As the load is increased, the speed of the DC Motor
a. Increases proportionately
b. Remains constant
c. Increases slightly
d. Reduces slightly……
14. Between no load and full load , ——– motor develops the least torque.
a. Series…….
b. Shunt
c. Cumulative compound
d. Differential compound
15. When load is removed, ——- motor will run at the highest speed.
a. Shunt
b. Cumulative compound
c. Differential compound
d. Series……
16. A series motor is best suited for driving
a. Lathes
b. Cranes and hoists……
c. Shears and punches
d. Machine tools
17. 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