1. What will be the current passing through the ring shaped air cored coil when number of
turns is 800 and ampere turns are 3200 ?
Correct : B. 4
2. What will be the magnetic potential difference across the air gap of 2 cm length in
magnetic field of 200 AT/m ?
Correct : B. 4 AT
3. A certain amount of current flows through a ring-shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil ?
Correct : B. Increases
4. The magnetic reluctance of a material
Correct : A. decreases with increasing cross sectional area of material
5. The initial permeability of an iron rod is
Correct : D. the permeability almost in non-magnetised state
6. How does the magnetic compass needle behave in a magnetic field ?
Correct : C. It assures a position which follows a line of magnetic flux
7. In a simple magnetic field the strength of magnet flux
Correct : D. first increases and then decreases till it becomes zero
8. The stray line of magnetic flux is defined as
Correct : D. a line of magnetic flux which does not follow the designed path
9. The bar magnet has
Correct : A. the dipole moment
10. Which of the following materials are dia-magnetic ?
Correct : C. Silver and copper
11. Which of the following type of materials are not very important for engineering
applications ?
Correct : C. Diamagnetic
12. The susceptibility of paramagnetic materials generally lies between
Correct : A. KT3 and 1CT6
13. For which of the following materials the saturation value is the highest ?
Correct : D. Ferrites
14. The magnetic materials exhibit the property of magnetisation because of
Correct : C. spin of nucleus
15. For which of the following materials the net magnetic moment should be zero ?
Correct : C. Antiferromagnetic materials
16. The attraction capacity of electromagnet will increase if the
Correct : D. flux density increases
17. Which of the following statements is correct ?
Correct : A. The conductivity of ferrites is better than ferromagnetic materials
18. Temporary magnets are used in
Correct : D. all of the above
19. Main causes of noisy solenoid are
Correct : C. both of above
20. Core of an electromagnet should have
Correct : C. both of the above
21. Magnetism of a magnet can be destroyed by
Correct : D. by all above methods
22. An air gap is usually inserted in magnetic circuits to
Correct : C. prevent saturation
23. The relative permeability of a ferromagnetic material is
Correct : D. more than 100 or 1000
24. The unit of magnetic flux is
Correct : B. weber
25. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
Correct : C. conductivity
26. Point out the wrong statement.
Magnetic leakage is undesirable in electric machines because it
Correct : A. lowers their power efficiency
27. Relative permeability of vacuum is
Correct : A. 1
28. Permanent magnets are normally made of
Correct : A. alnico alloys
29. Energy stored by a coil is doubled when its current is increased by percent.
Correct : C. 41.4
30. Those magnetic materials are best suited for making armature and transformer cores
which have____permeability and_______hystersis loss.
Correct : C. high, low
31. The rate of rise of current through an inductive coil is maximum
Correct : B. at the start of the current flow
32. When both the inductance and resistance of a coil are doubled the value of
Correct : A. time constant remains unchanged
33. The initial rate of rise of current through a coil of inductance 10 H when suddenly
connected to a D.C. supply of 200 V is_______Vs
Correct : B. 20
34. A material for good magnetic memory should have
Correct : D. high retentivity
35. Conductivity is analogous to
Correct : C. permeability
36. In a magnetic material hysteresis loss takes place primarily due to
Correct : D. it high retentivity
37. Those materials are well suited for making permanent magnets which
have______retentivity and _______coercivity.
Correct : B. high, high
38. If the area of hysteresis loop of a material is large, the hysteresis loss in this material
will be
Correct : C. large
39. Hard steel is suitable for making permanent magnets because
Correct : A. it has good residual magnetism
40. Silicon steel is used in electrical machines because it has
Correct : C. low hysteresis loss
41. Conductance is analogous to
Correct : A. permeance
42. The property of a material which opposes the creation of magnetic flux in it is known as
Correct : D. reluctance
43. The unit of retentivity is
Correct : B. weber/sq. m
44. Reciprocal of reluctance is
Correct : B. permeance
45. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared
with which parameter of electrical circuit ?
Correct : B. Current
46. The unit of reluctance is
Correct : D. 1/henry
47. A ferrite core has less eddy current loss than an iron core because
Correct : D. ferrites have high hysteresis
48. Hysteresis loss least depends on
Correct : D. ambient temperature
49. Laminated cores, in electrical machines, are used to reduce
Correct : B. eddy current loss
50. The property of coil by which a counter e.m.f. is induced in it when the current through
the coil changes is known as
Correct : A. self-inductance
51. As per Faraday's laws of electromagnetic induction, an e.m.f. is induced in a conductor
whenever it
Correct : C. cuts magnetic flux
52. Which of the following circuit element stores energy in the electromagnetic field ?
Correct : A. Inductance
53. The inductance of a coil will increase under all the following conditions except
Correct : A. when more length for the same number of turns is provided
54. Higher the self-inductance of a coil,
Correct : D. longer the delay in establishing steady current through it
55. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil.
The inductance of the coil will
Correct : B. decrease
56. An open coil has
Correct : B. infinite resistance and zero inductance
57. Both the number of turns and the core length of an inductive coil are doubled.
Its self-inductance will be
Correct : B. doubled
58. If current in a conductor increases then according to Lenz's law self-induced voltage will
Correct : C. produce current opposite to the in-creasing current
59. The direction of incViced e.m.f. can be found by
Correct : B. Lenz's law
60. Air-core coils are practically free from
Correct : C. both (a) and (b)
61. The magnitude of the induced e.m.f. in a conductor depends on the
Correct : D. rate of change of flux-linkages
62. Mutually inductance between two magnetically-coupled coils depends on
Correct : D. all of the above
63. A laminated iron core has reduced eddy-current losses because
Correct : B. the laminations are insulated from each other
64. The law that the induced e.m.f. and current always oppose the cause producing them is
due to
Correct : B. Lenz
65. Which of the following is not a unit of inductance ?
Correct : B. Coulomb/volt ampere
66. In case of an inductance, current is proportional to
Correct : B. magnetic field
67. Which of the following circuit elements will oppose the change in circuit current ?
Correct : B. Inductance
68. For a purely inductive circuit which of the following is true ?
Correct : C. Actual power of the circuit is zero
69. Which of the following is unit of inductance ?
Correct : B. Henry
70. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current
must be
Correct : D. 4 A/s
71. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core
length is doubled, all other quantities, remaining the same, the in ductance will be
Correct : A. 3 mH
72. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is
0.5, the mutual inductance of the coils is
Correct : C. 6 mH
73. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If
the two coils are connected in series aiding, the total inductance will be
Correct : B. 38 mH
74. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400
turns, all other quantities (area, length etc.) remaining the same, the inductance will be
Correct : D. 48 mH
75. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If
the two coils are connected in series, the total inductance will be
Correct : C. 12 H
76. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling
will be
Correct : B. 1.0
77. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance
is
Correct : D. 5000 ohms
78. A conductor 2 metres long moves at right angles to a magnetic field of flux density 1
tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
Correct : C. 25V
79. Lenz's law is a consequence of the law of conservation of
Correct : C. energy
80. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla.
The force on the conductor will be nearly
Correct : B. 120 N
81. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right
angles to a magnetic field having a flux density of 0.67 tesla.
Correct : A. 100 N
82. The co-efficient of coupling between two air core coils depends on
Correct : C. mutual inductance and self inductance of two coils
83. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in
flux which occurs in 0.5 second. The total flux change is
Correct : D. 0.02 Wb
84. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time
interval must a flux change of 0.06 Wb occur to produce such a voltage ?
Correct : C. 0.5 s
85. Which of the fpllowing inductor will have the least eddy current losses ?
Correct : A. Air core
86. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of
inductance is
Correct : B. 350 mH
87. Two 300 uH coils in series without mutual coupling have a total inductance of
Correct : B. 600 uH
88. Current changing from 8 A to 12 A in one second induced 20 volts in a coil.
The value of inductance is
Correct : C. 5 H
89. Which circuit element(s) will oppose the change in circuit current ?
Correct : B. Inductance only
90. A crack in the magnetic path of an inductor will result in
Correct : D. reduced inductance
91. A coil is wound on iron core which carries current I. The self-induced voltage in the coil
is not affected by
Correct : B. variation in voltage to the coil
92. The polarity of the induced voltage can be determined by using the left-hand generator
rule.
Correct : A. Yes
93. Increasing the field or increasing the current will decrease the force on the conductor.
Correct : B. No
94. Reversing the field or the current will reverse the force on the conductor.
Correct : A. Yes
95. When a conductor moves in the field, so that it makes an angle 8 with the lines of flux,
the force F is given as : F = Bl sin2 0.
Correct : B. No
96. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts
when the current in the circuit changes at the rate of unit weber turns.