HAL Placement Papers - Electronics and Electrical questions

HAL Placement Papers - Electronics and Electrical questions

The HAL Electronics and Electrical written test is an online test, in which objective type of questions are asked with a time limit of mostly 2 ½ hours.

Here are a few questions asked in the Electronics and Electrical section of HAL written test:

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

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

3. In lap winding, how many numbers of brushes are used always?
(a) two
(b) same as the number of poles
(c) half the number of poles
(d) double the number of poles

4. 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) Wave winding
(b) Lap winding
(c) Either of (a) and (b) above
(d) Depends on other features of design

5. What are Laminations of core are made of generally?
(a) carbon
(b) silicon steel
(c) cast iron
(d) stainless steel

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

7. Why is the armature of D.C. generator laminated?
(a) provide the bulk
(b) reduce the bulk
(c) insulate the core
(d) reduce eddy current loss

8. On what does the resistance of armature winding depends?
(a) cross-sectional area of the conductor
(b) length of conductor
(c) number of conductors
(d) all of the above

9. What are the field coils of D.C. generator usually made of?
(a) Copper
(b) Mica
(c) Cast iron
(d) Carbon

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

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

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

13. 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) lines of force
(b) motion of conductor
(c) either of the above
(d) none of the above

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

15. 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

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

17. Why are Copper brushes in D.C. machine 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. How is a separately excited generator as compared to a self-excited generator better?
(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) speed
(b) voltage
(c) current
(d) friction

20. How is Iron loss in a D.C. machine are independent of variations in?
(a) Speed and voltage
(b) load
(c) voltage
(d) speed

21. In D.C. generators, current to the external circuit from armature is given through
(a) commutator
(b) slip rings
(c) solid connection
(d) none of above

22. What are the Brushes of D.C. machines made of?
(a) soft copper
(b) carbon
(c) hard copper
(d) all of above

23. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Bl2v
(b)Blv2
(c)Blv
(d)Bl2v2

24. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 8
(b) 4
(c) 32
(d) 16

25. What is the material used in commutator brushes?
(a) carbon
(b) copper
(c) cast iron
(d) Mica

26. What is the insulating material used between the commutator segment is?
(a) Graphite
(b) mica
(c) paper
(d) insulating varnish

27. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a) lie under south pole
(b) lie under north pole
(c) are farthest from the poles
(d) lie under interpolar region

28. Which of the following statement about D.C. generators is false ?
(a) Compensating winding in a D.C. machine helps in commutation
(b) In a D. C. generator interpoles winding is connected in series with the armature winding
(c) Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d) Equilizing bus bars are used with parallel running of D.C. shunt generators

29. What does the demagnetising component of armature reaction in a D.C. generator do?
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble

30. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above

31. On what does the number of brushes in a commutator depends on?
(a) speed of armature
(b) voltage
(c) type of winding
(d) amount of current to be collected

32. Compensating windings are used in D.C. generators
(a) mainly to reduce the eddy currents by providing local short-circuits
(b) to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction
(d) none of the above

33. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator?
(a) Eye bolt
(b) Commutator
(c) Dummy coils
(d) Equilizer rings

34. In a D.C. generator, how are the ripples in the direct e.m.f. generated reduced by?
(a) using conductor of annealed copper
(b) using commutator with large number of segments
(c) using carbon brushes of superior quality
(d) using equiliser rings

35. In D.C. generators, what is lap winding is used for?
(a) high voltage, high current
(b) low voltage, high current
(c) low voltage, low current
(d) high voltage, low curreny

36. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 1 : 3
(b) 3 : 2
(c) 3 : 1
(d) 2 : 3

37. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Carbon brushes
(b) Graphite brushes
(c) Metal graphite brushes
(d) None of the above

38. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
(a) demagnetisation only
(b) cross magnetisation as well as demagnetisation
(c) cross magnetisation as well as magnetising
(d) cross magnetisation only

39. What is the armature reaction of an unsaturated D.C. machine?
(a) cross magnetising
(b) demagnetising
(c) magnetising
(d) none of above

40. D.C. generators are connected to the bus bars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the prime mover
(b) to avoid mechanical jerk to the shaft
(c) to avoid burning of switch contacts
(d) all above

41. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature
(d) all above

42. In a D.C. machine, short-circuited field coil will result in
(a) odour of barning insulation
(b) unbalanced magnetic pull producing vibrations
(c) reduction of generated voltage for which excitation has to be increased to maintain the voltage
(d) all above

43. Why is equilizer rings required in case of armature?
(a) wave wound
(b) lap wound
(c) delta wound
(d) duplex wound

44. What does welding generator has
(a) lap winding
(b) wave winding
(c) delta winding
(d) duplex wave winding

45. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns

46. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a) induction motor D.C. generator set
(b) mercury are rectifier
(c) rotary converter
(d) synchronous motor D.C. generator set

47. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the magnetic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions

48. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches

49. What does the A D.C. welding generator has?
(a) duplex winding
(b) wave moving
(c) lap winding
(d) any of the above

50. What happens when length of wire increases its resistance also?
(a) half
(b) doubles
(c) remains the same
(d) none of the above