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Electrical Engineering
D.C. Motors
Quiz 4
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Q.1
D.C. generators are normally designed for maximum efficiency around
Full load
Rated r.p.m.
Rated voltage
All of the above
Q.2
Three point starter can be used for
Series motor only
Shunt motor only
Compound motor only
Both shunt and compound motor
Q.3
These days D.C. motors are widely used in
Pumping sets
Air compressors
Electric traction
Machine shops
Q.4
In D.C. shunt motors as load is reduced
The speed will increase abruptly
The speed will increase in proportion to reduction in load
The speed will remain almost/constant
The speed will reduce
Q.5
What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
The motor will stop
The motor will continue to run
The armature may burn
The motor will run noisy
Q.6
If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
This will make armature to take heavy current, possibly burning it
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
Nothing will happen to motor
Motor will come to stop
Q.7
If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
Nothing will happen to the motor
This will make armature to take heavy current, possibly burning it
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
Motor will run at very slow speed
Q.8
Differentially compound D.C. motors can find applications requiring
High starting torque
Low starting torque
Variable speed
Frequent on-off cycles
Q.9
At the instant of starting when a D.C. motor is put on supply, it behaves like
A highly resistive circuit
A low resistance circuit
A capacitive circuit
None of the above
Q.10
Which D.C. motor has got maximum self relieving property?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor
Q.11
The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
2.36%
4.76%
6.77%
8.84%
Q.12
For a D.C. shunt motor if the excitation is changed
Torque will remain constant
Torque will change but power will remain constant
Torque and power both will change
Torque, power and speed, all will change
Q.13
A three point starter is considered suitable for
Shunt motors
Shunt as well as compound motors
Shunt, compound and series motors
All D.C. motors
Q.14
The main disadvantage of the Ward-Leonard control method is
High initial cost
High maintenance cost
Low efficiency at high loads
All of the above
Q.15
For the same H.P. rating and full load speed, following motor has poor starting torque
Shunt
Series
Differentially compounded
Cumulatively compounded
Q.16
Which D.C. motor is generally preferred for cranes and hoists?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor
Q.17
One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
Runs as a generator
Does not run as a generator
Also runs as a motor comes to stop after sometime
None of these
Q.18
Which D.C. motor has got maximum self loading property?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor
Q.19
In D.C. machines the residual magnetism is of the order of
2 to 3 percent
10 to 15 percent
20 to 25 percent
50 to 75 percent
Q.20
In a D.C. generator, the iron losses mainly take place in
Yoke
Commutator
Armature conductors
Armature rotor
Q.21
Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
Drum type controller is used
Three point starter is used
Four point starter is used
All above can be used
Q.22
Ward-Leonard control is basically a
Voltage control method
Field diverter method
Field control method
Armature resistance control method
Q.23
For constant torque drive which speed control method is preferred?
Field control
Armature voltage control
Shunt armature control
Mechanical loading system
Q.24
By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
Frame
Shaft
Commutator
Stator
Q.25
Which of the following motors is most suitable for signalling devices and many kinds of timers ?
D.C. shunt motor
D.C. series motor
Induction motor
Reluctance motor
Q.26
The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
4.0
2.0
1.0
0.5
Q.27
When two D.C. series motors are connected in parallel, the resultant speed is
More than the normal speed
Loss than the normal speed
Normal speed
Zero
Q.28
Which of the following losses are significantly reduced by laminating the core of a D.C. generator?
Hysteresis losses
Eddy current losses
Copper losses
Windage losses
Q.29
In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
100%
Around 90%
Anywhere between 75% and 90%
Less than 50%
Q.30
The direction of rotation of a D.C. series motor can be changed by
Interchanging supply terminals
Interchanging field terminals
Either of (A) and (B) above
None of the above
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