Consider the following statements regarding dc machines : 1. possible resistance of shunt-field winding is 1 Ω 2. possible resistance of series-field winding is 1 Ω 3. electrographite brushes are used for 230 V, 10 A machines 4. Copper-graphite brushes are used for 230 V, 10 A machines 5. Possible armature-circuit resistance is 1 Ω From these, the correct statements are

Electrical Machines
Consider the following statements regarding dc machines : 1. possible resistance of shunt-field winding is 1 Ω 2. possible resistance of series-field winding is 1 Ω 3. electrographite brushes are used for 230 V, 10 A machines 4. Copper-graphite brushes are used for 230 V, 10 A machines 5. Possible armature-circuit resistance is 1 Ω From these, the correct statements are

1, 4

1, 3, 5

2, 4 ,5

2, 3 , 5

1, 4

1, 3, 5

2, 4 ,5

2, 3 , 5

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Electrical Machines
With the increase in speed of a DC motor

back emf falls and line current increases.

both back emf as well as line current fall.

back emf increases but line current falls.

both back emf as well as line current increase.

back emf falls and line current increases.

both back emf as well as line current fall.

back emf increases but line current falls.

both back emf as well as line current increase.

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Electrical Machines
In a dc machine 4 pole lap winding is used. The number of parallel paths are?

8

4

1

2

8

4

1

2

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Electrical Machines
For 250 volt DC Shunt Motor the armature and field resistance are 0.5 ohm and 250 ohm respectively. What will be the back e.m.f. produced when it takes a load current of 21A.

220 V.

280 V.

240 V.

150 V.

220 V.

280 V.

240 V.

150 V.

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Electrical Machines
DC motors are stopped by opening line switches and not by forcing the handle of the motor starter back to OFF position. This is due to occurance of

Both of above.

Heavy sparking at brushes.

None of these.

Heavy sparking at the first stud of starting resistance steps.

Both of above.

Heavy sparking at brushes.

None of these.

Heavy sparking at the first stud of starting resistance steps.

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Electrical Machines
The commutator segments of DC machines are made up of

copper alloy

hard-drawn copper

copper

brass

copper alloy

hard-drawn copper

copper

brass

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Electrical Machines

Electrical Machines With the increase in speed of a DC motor

Electrical Machines In a dc machine 4 pole lap winding is used. The number of parallel paths are?

Electrical Machines For 250 volt DC Shunt Motor the armature and field resistance are 0.5 ohm and 250 ohm respectively. What will be the back e.m.f. produced when it takes a load current of 21A.

Electrical Machines DC motors are stopped by opening line switches and not by forcing the handle of the motor starter back to OFF position. This is due to occurance of

Electrical Machines The commutator segments of DC machines are made up of

Electrical Machines
With the increase in speed of a DC motor

Electrical Machines
In a dc machine 4 pole lap winding is used. The number of parallel paths are?

Electrical Machines
For 250 volt DC Shunt Motor the armature and field resistance are 0.5 ohm and 250 ohm respectively. What will be the back e.m.f. produced when it takes a load current of 21A.

Electrical Machines
DC motors are stopped by opening line switches and not by forcing the handle of the motor starter back to OFF position. This is due to occurance of

Electrical Machines
The commutator segments of DC machines are made up of