MCQ on DC generator 1-20

1. Laminations of core are generally made of
(a) case iron
(b) carbon
(c) silicon steel✔
(d) stainless steel

2. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m✔
(d) 5 m

3. The armature of D.C. generator is laminated to
(a) reduce the bulk
(b) provide the bulk
(c) insulate the core
(d) reduce eddy current loss✔

4. The resistance of armature winding depends on
(a) length of conductor
(b) cross-sectional area of the conductor
(c) number of conductors
(d) all of the above✔

5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper✔
(c) cast iron
(d) carbon

6. The commutator segments are connected to the armature conductors by means of
(a) copper lugs✔
(b) resistance wires
(c) insulation pads
(d) brazing

7. In a commutator
(a) copper is harder than mica
(b) mica and copper are equally hard
(c) mica is harder than copper✔
(d) none of the above

8. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets
(b) counter sunk screws✔
(c) brazing
(d) welding

9. According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor
(b) lines of force✔
(c) either of the above
(d) none of the above

10. Fleming’s right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force
(b) magnetic flux, direction of motion and the direction of e.m.f. induced✔
(c) magnetic field strength, induced voltage and current
(d) magnetic flux, direction of force and direction of motion of conductor

11. While applying Fleming’s right-hand rule to And the direction of induced e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(d) direction of motion of conductor, if✔ forefinger points along the lines of flux

12. The bearings used to support the rotor shafts are generally
(a) ball bearings✔
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings

13. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above✔

14. In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles✔
(c) half the number of poles
(d) two

15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
(a) Lap winding
(b) Wave winding✔
(c) Either of (a) and (b) above
(d) Depends on other features of design

16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south✔
(c) all the four poles are south poles
(d) two north poles follow two south poles

17. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved✔
(b) where high voltage and small cur-rents are involved
(c) in both of the above cases
(d) in none of the above cases

18. A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage control
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features✔

19. In case of D.C. machines, mechanical losses are primary function of
(a) current
(b) voltage
(c) speed✔
(d) none of above

20. Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load✔
(c) voltage
(d) speed and voltage