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- 1. Multiple Choice
The rotating part of a DC Motor is known as __________.
Pole
Stator
Armature
Carbon brush
- 2. Multiple Choice
Carbon brushes are used on DC Motors to __________.
Brush off carbon deposits
Provide a path for flow of current
Prevent sparking during commutation
Prevent overheating of armature winding
- 3. Multiple Choice
Voltage equation for DC Motor is __________.
V = Eb + IaRa
V = Eb – IaRa
Eb = V – IfRf
Eb = V + IaRa
- 4. Multiple Choice
Condition for maximum power output for DC Motor is __________.
Et = V
Eb = V/2
Eb = IaRa/2
Eb = IaRa + IfRf
- 5. Multiple Choice
The speed of a DC Motor is __________.
Directly proportional to EMF as well as flux
Inversely proportional to EMF as well as flux
Directly proportional to back EMF and inversely proportional to flux
Inversely proportional to back EMF and directly proportional to flux
- 6. Multiple Choice
The highest speed attained by DC shunt motor is __________.
Higher than no-load speed at rated flux
Lower than no-load speed at rated flux
Equal to no-load speed at rated flux
Equal to infinity at rated flux
- 7. Multiple Choice
In a DC Motor iron losses occurs in the __________.
Yoke
Field
Armature
None of these
- 8. Multiple Choice
The dummy coil in the DC machines is used to __________.
Eliminate reactance voltage
Eliminate armature reaction
Eliminate harmonics developed in the machine
Bring about mechanical balance of armature
- 9. Multiple Choice
And external resistance is added in series with the field of a DC shunt motor. When the motor runs, the effect of resistance is __________.
To increase the speed of the motor
To reduce the losses
To reduce the speed of the motor
To reduce the armature current of the motor
- 10. Multiple Choice
The speed of a dc shunt motor is required to be more than full load speed. This is possible by __________.
Increasing the excitation current
Increasing the armature current
Decreasing to armature current
Reducing the field current
- 11. Multiple Choice
If speed of a DC shunt motor increases, the back EMF __________.
Increases
Decreases
Decreases and then increases
Remains constant
- 12. Multiple Choice
As the load is increased, the speed of a DC shut motor will __________.
Increase slightly
Increase proportionately
Remain constant
Reduce slightly
- 13. Multiple Choice
The current drawn by the armature of a DC shunt motor is __________.
Eb/Ra
V/Ra
(V – Eb)/Ra
(Eb - V)/ Ra
- 14. Multiple Choice
If the current in the armature of a DC series motor is reduced to 50% the torque of the motor will become __________.
25% of the previous value
50% of the previous value
75% of the previous value
150% of the previous value
- 15. Multiple Choice
The shunt field current flowing in a short shunt compound DC Motor is given by __________.
Ish = V/Rsh
Ish = (V + Isc Rsc)/Rsh
Ish = V – (Isc Rsc ) /Rsh
None of these
- 16. Multiple Choice
In DC shunt motor, if the terminal voltage is reduced to half and torque remains the same, then __________.
Speed and armature will be the same
Speed will be half but armature current remains the same
Speed will be half and armature current also will be half
Speed will be half and armature current becomes double
- 17. Multiple Choice
One DC Motor drives another DC Motor. The second DC Motor when excited and driven __________.
Heats excessively
Also runs as a motor
Runs as a generator
None of these
- 18. Multiple Choice
A 4 pole, simplex lap wound armature has 400 conductors and flux per pole of 25 mWb. The emf generated when running at 600 rpm, will be __________ V.
30
60
100
240
- 19. Multiple Choice
The torque of a motor is __________.
The force acting on the motor
The electrical power of the motor
The tangential force on the rotor multiplied by the rotor radius
None of these
- 20. Multiple Choice
The output power of any electrical motor is taken from the __________.
Poles
Armature
Conductors
Coupling mounted on the shaft
- 21. Multiple Choice
The power stated on the nameplate of any motor is always the __________.
Gross power
Power drawn in KW
Power drawn in KVA
Output power at the shaft
- 22. Multiple Choice
A starter is necessary to start a DC Motor because it __________.
Starts the motor
Limits the motor speed
Limits the EMF to a sale value
Limits the starting current to s safe value
- 23. Multiple Choice
The direction of rotation of a DC Motor is reversed by __________.
Reversing supply connection
Reversing armature connection
Adding resistance to the field circuit
Interchanging the armature and field connection
- 24. Multiple Choice
Which of the ff is a correct statement about a series motor?
It has a poor torque
It can run easily without load
It has an almost constant speed
The field winding consists of thicker wire and less turns
- 25. Multiple Choice
Which of the ff DC Motors has the least drop in speed between no-load and nominal load?
Shunt motor with commutating poles
Series motor with commutating poles
Series motor without commutating poles
Compound motor without commutating poles
- 26. Multiple Choice
The speed of a series motor at no-load is __________.
zero
Infinity
3,000 rpm
3,600 rpm
- 27. Multiple Choice
The speed of a DC series motor decreases if the flux in the field winding __________.
Increases
Decreases
Remains constant
None of these
- 28. Multiple Choice
Which of the ff motors is used to drive the constant speed line shafting lathes, blowers and fans?
Series
Shunt
Cumulative compound
Differential compound
- 29. Multiple Choice
If the back EMF in a DC Motor is absent then __________.
Motor will burn
Motor will not run at all
Motor will run at very low speed
Motor will not run at very high speed
- 30. Multiple Choice
The field flux of a DC Motor can be controlled to achieve __________.
Speed higher than rated speed
Speeds lower than rated speed
Speed at rated load
None of these
- 31. Multiple Choice
By providing a variable resistance across the series field (diverter) in a DC series motor, speeds above normal can be obtained because __________.
Flux is reduced
Line current decreases
Armature current decreases
None of these
- 32. Multiple Choice
DC series motors are best suited for traction of work because __________.
Torque and speed are proportional to the square of the armature current
Torque is proportional to the square of the armature current and speed is proportional to the torque
Torque is proportional to the square of the armature current and speed is inversely proportional to the torque
None of these
- 33. Multiple Choice
A DC series motor is started without load. The effect is that __________.
The speed increases rapidly
The torque increases rapidly
The current drawn increases rapidly
The back EMF decreases
- 34. Multiple Choice
The direction of rotation of a DC series motor can be reversed by interchanging the __________.
Field terminals only
Supply terminals only
Supply as well as field terminals
None of these
- 35. Multiple Choice
The motor used for intermittent, high torque is __________.
Series motor
Shunt motor
Cumulative compound motor
Differential compound motor
- 36. Multiple Choice
If the field of a DC shunt motor is opened, then __________.
The motor will stop
It will continue to run at its rated speed
The speed of the motor will decrease
The speed of the motor will become very high
- 37. Multiple Choice
Which of the ff DC Motors is used for rolling mills?
Series motor
Shunt motor
Differential compound motor
Cumulative compound motor
- 38. Multiple Choice
Armature reaction is attributed to the __________.
Copper loss in the armature
Effect of magnetic field set-up by the back EMF
Effect of the magnetic field set-up by the field current
Effect of magnetic field set-up by the armature current
- 39. Multiple Choice
What will happen if the supply terminals of DC shunt motor are interchanged?
Motor will stop
The direction of rotation will be reversed
Motor will run at its normal speed in the same direction as it was running
Motor will run at lower speed than the normal speed in the same direction
- 40. Multiple Choice
When the electric train is moving down a hill, the DC Motor acts as DC __________.
Series motor
Shunt motor
Series generator
Shunt generator
- 41. Multiple Choice
Which of the ff DC Motors is suitable for high starting torque?
Series
Shunt
Cumulative compound
Differential compound
- 42. Multiple Choice
Which of the ff DC Motors is used for flywheel drive?
Series
Universal
Universal
Compound
- 43. Multiple Choice
Why is the air gap between the stator and armature of an electric motor kept as small as possible?
To make the rotation easier
To improve the air circulation
To get a stronger magnetic field
To reach a higher speed of rotation
- 44. Multiple Choice
Interpoles are meant for __________.
Converting armature current to DC
Increasing the speed of the motor
Decreasing counter EMF
Reducing sparking at the commutator
- 45. Multiple Choice
It is preferable to start a DC series motor with some mechanical load on it because __________.
It will not run at no-load
It acts as starter of the motor
It may develop excessive speed and damage itself
None of these
- 46. Multiple Choice
If the flux of a DC Motor approaches zero, its speed will approach __________.
Zero
Infinity
A stable value nearer to the rated speed
None of these
- 47. Multiple Choice
A 230 V DC series motor is connected to a 230 V AC supply. It will __________.
Burn
Run slowly
Run with less efficiency
Not run at all
- 48. Multiple Choice
Which of the ff statements is incorrect. If a starter is not used with large DC Motor, it will draw a starting current which __________.
Is many times the full load current
Will damage the commutator
Will produce excessive line voltage
Will produce very low starting torque
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