magnetism and electromagnetism Mcqs
51. The Biot-savarts law is a general modification of_______________?
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A. Faradays laws

B. Kirchhoffs law

C. Amperes law

D. Lenzs law

52. A keeper is used to_____________?
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A. provide a closed path for flux

B. restore lost flux

C. amplify flux

D. change the direction of magnetic lines

53. Core of an electromagnet should have____________?
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A. low coercivity

B. high susceptibility

C. both of the above

D. none of the above

54. What is the magnitude and the direction of force per 1.1m length of a pair of conductors of a direct current linecarrying 10 amperes and spaced 100 mm apart ?
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A. 22 x 10-6 N

B. 22 x 10?5 N

C. 22 x 10?8 N

D. 22 x 10?7 N

55. Which of the following statements is correct ?
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A. The conductivity of ferrites is better than ferromagnetic materials

B. The conductivity of ferrites is very high

C. The conductivity of ferrites is same as that of ferromagnetic materials

D. The conductivity of ferromagnetic materials is better than ferrites

56. Magnetising steel is normals difficult because____________?
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A. it has low permeability

B. it has high specific gravity

C. it corrodes easily

D. it has high permeability

57. The main constituent of permalloy is_____________?
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A. chromium

B. nickel

C. cobalt

D. tungsten

58. Indicate which of the following material does not retain magnetism permanently
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A. None of the above

B. Hardened steel

C. Stainless steel

D. Soft iron
59. The electromagnet has 50 turns and a current of 1A flows through the coil. If the length of the magnet circuit is 200 mm, what is the magnetic field strength ?
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A. 2.5 AT/m

B. 2500 AT/m

C. 250 AT/m

D. 25 AT/m

60. When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the center of the circle?
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A. will depend on the amount of e.m.f. applied

B. will be zero

C. will be infinite

D. will depend on the radius of the circle
61. The commonly used material for shielding or screening magnetism is____________?
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A. aluminium

B. copper

C. soft iron

D. brass

62. The magnetism left in the iron after exciting field has been removed is known as____________?
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A. susceptance

B. reluctance

C. permeance

D. residual magnetism
63. A 200 turn coil having an axial length of 30 mm and a radius of 10 mm is pivoted in a magnetic field having a flux density of 0.8 T. If the coil carries a current of 0.5 A, the torque acting on the coil will be_____________?
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A. 0.0048 N-m

B. 0.048 N-m

C. 0.48 N-m

D. 8 N-m

64. The left hand rule correlates to______________?
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A. self induction, mutual induction and direction of force on a conductor

B. current, magnetic field and direction of force on a conductor

C. magnetic field, electric field and direction of force on a conductor

D. current, induced e.m.f. and direction of force on a conductor

65. The use of permanent magnets is. not made in_____________?
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A. energy meters

B. loud-speakers

C. transformers

D. magnetoes

66. The uniform magnetic field is______________?
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A. the field in which all lines of magnetic flux are parallel and equidistant

B. the field of a set of parallel conductors

C. none of the above

D. the field of a single conductor

67. The unit of relative permeability is_____________?
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A. it is dimensionless

B. henry/sq. m

C. henry/metre

D. henry

68. Which of the following is expected to have the maximum permeability ?
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A. Ebonite

B. Copper

C. Brass

D. Zinc

69. Which of the following statements is correct ?
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A. The magnetic flux inside the exciting coil is same as on its outside surface

B. The magnetic flux inside an exciting coil is zero

C. The magnetic flux inside an exciting coil is lower than its outside surface

D. The magnetic flux inside the exciting coil is greater than its outside surface

70. Which of the following materials are diamagnetic ?
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A. Silver

B. Copper

C. Iron

D. Silver and copper
71. The force between two long parallel conductors is inversely proportional to_____________?
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A. radius of conductors

B. current in one conductor

C. distance between the conductors

D. product of current in two conductors

72. One maxwell is equal to____________?
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A. 10 webers

B. 10 webers

C. 10 webers

D. 10 webers

73. he retentivity (a property) of material is useful for the construction of_______________?
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A. electromagnets

B. permanent magnets

C. non-magnetic substances

D. transformers

74. The magnetic reluctance of a material______________?
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A. decreases with increasing cross sectional area of material

B. does not vary with increasing cross-sectional area of material

C. any of the above

D. increases with increasing cross-sec-tional area of material

75. A 300 mm long conductor is carrying a current of 10 A and is situated at right angles to a magnetic field having a flux density of 0.8 T ; the force on the conductor will be____________?
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A. 240 N

B. 0.24 N

C. 2.4 N

D. 24 N

76. Which of the following is a ferromagnetic material ?
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A. Tungsten

B. Copper

C. Aluminium

D. Nickel
77. The susceptibility of paramagnetic materials generally lies between____________?
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A. 1CT3 and 1CT7

B. 10?2 and KT5

C. KT4 and KT8

D. KT3 and 1CT6
78. Ferrites are a sub-group of_______________?
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A. ferro-magnetic materials

B. paramagnetic materials

C. ferri-magnetic materials

D. non-magnetic materials

79. The unit of flux is the same as that of_______________?
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A. resistance

B. reluctance

C. pole strength

D. permeance

80. Flemings left hand rule is used to find_________________?
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A. direction of flux in a solenoid

B. direction of magnetic field due to current carrying conductor

C. polarity of a magnetic pole

D. direction of force on a current carrying conductor in a magnetic field
81. Main causes of noisy solenoid are______________?
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A. strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force

B. uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts

C. both of above

D. none of the above

82. When a magnet is in motion relative to a coil the induced e.m.f. does not depend upon____________?
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A. number of turns of the coil

B. motion of the magnet

C. resistance of the coil

D. pole strength of the magnet

83. Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials
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A. triangular

B. circular

C. rectangular

D. none of the above

84. What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m ?
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A. 6 AT

B. 4 AT

C. 2 AT

D. 10 AT

85. Paramagnetic materials have relative permeability________________?
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A. equal to unity

B. slightly more than unity

C. slightly less than unity

D. equal to that ferromagnetic mate rials

86. For which of the following materials the net magnetic moment should be zero ?
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A. Ferrimagnetic materials

B. Diamagnetic materials

C. Antiferromagnetic materials

D. Antiferrimagnetic materials