PHYSICS: D.C. MACHINE 03/08 Online Test

In a D.C machine constant losses composed of
Mechanical losses
Commutator losses
Iron losses and mechanical losses
Total copper losses of the machine
In a D.C machine variable losses are composed of
Iron losses
Mechanical losses
Shunt field copper losses
Armature copper losses
If the resistance of the field winding of a D.C. generator is increased, the output voltage will
Fluctuate leavily
Remain unaffected
Increase
Decrease
Witch of the following D.C. generators can build up without any residual magnetism in the poles?
Compound generator
Shunt generator
Series generator
None of the above
Two series motors are mechanically coupled. One machine is run as motor and the other as generator The iron and friction losses of the machines will be identical when
Their speeds and excitations are identical
Their speeds are equal and back emf are half the supply voltage
Their ratings and armature sizes are identical
Their speeds are identical
In the block diagram of a separately excited D.C motor, the armature induced e.m.f appears as
Disturbance input
Positive feedback
Negative feedback
Output
Stray losses in D.C machine are
windage loss
Magnetic losses
Mechanical losses
All of the above
Which of the following statement is true while starting a D.C shunt motor:
Reduced armature voltage but full field voltage should be applied and all regulator resistance should be cut out in the field circuit
Rated armature and rated field voltage should be applied and full regulator resistance should be included in the field circuit
Reduced armature voltage and reduced field voltage should be applied and full regulator resistance should be included in the field circuit
Rated armature and rated filed voltage should be applied and full regulator resistance should be cut out on the field circuit
Which of the following type of D.C motor is least used?
Series motor
Differentially compound motor
Permanent magnet motor
Cumulative compound motor
Which of the following parts of a D.C motor can sustain the maximum temperature rise?
Slip rings
commutator
Field windings
Armature windings
In a D.C machine constant losses composed of
Mechanical losses
commutator losses
Iron losses and mechanical losses
Total copper losses of the machine
In a D.C machine variable losses are composed of
Iron losses
Mechanical losses
Shunt field copper losses
Armature copper losses
If the resistance of the field winding of a D.C. generator is increased, the output voltage will
Fluctuate heavy
Remain unaffected
Increase
Decrease
Witch of the following D.C. generators can build up without any residual magnetism in the poles?
Compound generator
Shunt generator
Series generator
None of the above
Brushes in D.C machines are always placed along
Geometrical neutral axis (GNA)
Magnetic neutral axis (MNA)
(1) And (2) both
None of the above
Brushes used in D.C machines are generally made of
Steel
Carbon
Brass
Copper
In a flat compound D.C. generator,
Speed varies in direct proportion to the load on the generator
Voltage generated reduces with load
Voltage remains constant irrespective of the load
Generated voltage is inversely proportional to the load on the generator
Over compounding of D.C generator, leads the full load terminal voltage to
Be less than no-load terminal voltage
Be more than no-load terminal voltage
Be equal to no-load terminal voltage
Almost zero
A D.C. motor is running with a certain load. The effect of adding an external resistance in the shunt Field circuit, load hewing constant, is
To stop the motor
To increase the motor speed
To reduce the motor speed
To reduce armature current of motor
A D.C shunt motor is running at a particular speed, it is desired to reverse its direction of rotation this can be achieved by
Providing reactifier
Reversing the field connections
Reversing the connections of the supply
Reversing the connections of field winding and armature
In the commutation process
Voltage is reversed
Current is reversed in the field coil
Current is reversed in the armature coil undergoing commutation
Both armature current and voltage are reversed
Description:

This is test is a part of a series of eight test which helps students to check the level of knowledge in Electricity, specifically in the DC Machine in Physics.

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