D.C generator. Part – 2

 

11. The EMF produced in a dc generator is _____ EMF

A. Statically

B. Dynamically

C. Magnetically

D. Electrostatically

12. In large dc generator, the magnetic field is produced by

A. Permanent magnet

B. Electro-magnet

C. either A or B 

D. none of these

13. The function of brushes in a dc generator is to

A. Collect the current from commutator and supply it to external circuit

B. Prevent sparking

C. Keep the commutator clean

D. Convert ac into dc

14. Lap winding is most suitable to

A. Low voltage, high current machine

B. High voltage, high current machine

C. High voltage, low current machine

D. Low voltage, low current machine

15. In a dc machine, which loss increases rapidly with the increase in frequency of magnetic reversals?

A. Copper loss

B. Mechanical loss

C. Eddy current loss

D. All of above

16. Brushes of D.C. machines are made of

A. Carbon

B. Soft copper

C. Hard copper

D. All of the above

17. The purpose of providing dummy coils in a generator is

A. To reduce eddy current losses

B. To enhance flux density

C. To amplify voltage

D. To provide mechanical balance for the rotor

18. Iron losses in a D.C. machine are independent of variations in

A. Speed

B. Load

C. Voltage

D. Speed and voltage

19. A D.C. generator works on the principal

A. Lenz’s law

B. Ohm’s law

C. Faraday’s law of electromagnetic induction

D. None of the above

20. A D.C. generator can be considered as

A. Rectifier

B. Prime mover

C. Rotating amplifier

D. Power pump