DC Machine: Physics Online Test

In an unsaturated D.C. machine armature reaction is
Magnetizing
Demagnetizing
Cross magnetizing
None of the above
Brushes of D.C. machines are usually made of
Hard copper
Soft copper
Carbon
All of the above
Which of the following factors does not govern the iron losses in a D.C. machine?
Load
Voltage
Speed
Speed and voltage
In the output voltage of a D.C.. Generator the ripple effects can be reduced by increasing the
Field current
Number of armature coils
Number of turns in the field winding
Size of the conductor of the armature coil
The armature core of, a D.C Machine is usually made of laminated sheets in order to
Reduce hysteresis loss
Reduce armature copper losses
Reduce eddy current
Increase its surface area for better dissipation of heat
Short circuited armature coil of a D.C. machine can be identified by
A spark completely around the commutator
The scanning of the commutator segment to which open circuited coil is connected
Both (a) and (b)
None of the above
The polarity of the inter poles in D.C generator
Is neutral as these poles do not play part in generating e.mJ
Is the same as that of the main pole ahead
Is the same as that of the immediately preceding pole
Is opposite to that of the main pole ahead
With given power rating for lower current and higher voltage rating of a d.c. Machine. One should prefer
Lap winding
Wave winding
None of these
Any of these
The compound generator is said to be flat compounded if the full load voltage is
More than the no-load voltage
Less than the no-load voltage
Exactly half of the no-load voltage
Equal to no-load voltage
In a D.C generator is run 'with different modes of field excitation keeping the no-load voltage constant at 250 V every time. The full-load voltages for the various connections are 250. 230. 215 and 180 V. The machines have following modes of excitation respectively
Cumulative compound, separately excited. Shunt and differential compound
Cumulative compound, separately excited, differential compound and shunt
Separately excited, cumulative compound, shunt and differential compound
Cumulative compound, differential compound, separately excited and shunt
The decrease in terminal voltage of a shunt generator, from no-load to load condition is due to
Decrease in field current
Armature reaction
Armature resistance drop
All of these
Commutation in a D.C generator causes
D.C changes to A.C.
D.C changes to D.C
A.C. changes to D.C.
A.C changes to high voltage D.C.
/
Only (iii) has to be satisfied
Only (i) and (ii) have to be satisfied
Only (i) and (iii) have to be satisfied
All the above condition have to be satisfied
In D.C. machines, lap winding is used for
Low voltage, low current
Low voltage, high current
High voltage, low current
High voltage, high current
Fractional pitch winding is used in D.C machine
To reduce sparking
To save the copper because of shorter end connections
To increase the generated voltage
Due to (a) and.(b) above
The yoke of a D.C machine is made up of
Copper-zinc alloy
Insulating material
Comparatively poor magnetic material
Very high permeability magnetic material
The commutator segments of a D.C machine are usually made of
Carbon
Iron.
Hard drawn copper
Stainless steel.
The e.m.f generated in the armature of D.C generator is directly proportional to
Number of poles
Speed of armature
Flux/pole
All of the above
In the armature, D.C. generator generates
Oscillating e.m.f
A.C. Voltage
A.C. Superimposed over D.C
D.C. Voltage
The characteristic drawn between no-load generated e.m.f. And the field current is known as
Magnetizing characteristic
External characteristic
Internal characteristic
Total characteristic
Description:

This is a Physics Test. The questions here are covered form the chapters of Magnetic Effect of Electric Current. Specifically, DC Machine and related topics are included.

Discussion

k.rama krishna

fst than u.... and good logical quentions.........

3349 days 1 hours 5 minutes ago

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