Objective Magnetism and Electromagnetism Questions and Answers pdf

61.   The most effective and quickest may of making a magnet from soft iron is by
(a)     placing it inside a coil carrying current
(b)     induction
(c) the use of permanent magnet
(d) rubbing with another magnet
Ans: a

62. The commonly used material for shielding or screening magnetism is
(a) copper
(b) aluminium
(c) soft iron
(d) brass
Ans: c

63. If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity
(a)     less than that of disc but in opposite direction
(b)     equal to that of disc and in the same direction
(c) equal to that of disc and in the opposite direction
(d) less than that of disc and in the same direction
Ans: d

64. A permanent magnet
(a) attracts some substances and repels others
(b) attracts all paramagnetic substan¬ces and repels others
(c) attracts only ferromagnetic sub¬stances
(d) attracts ferromagnetic substances and repels all others
Ans: a

65. The retentivity (a property) of material is useful for the construction of
(a) permanent magnets
(b) transformers
(c) non-magnetic substances
(d) electromagnets
Ans: a

66. The relative permeability of materials is not constant.
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) insulating
Ans: c

67. The materials are a bit inferior conductors of magnetic flux than air.
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) dielectric
Ans: c

68. Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials.
(a)     circular
(b)     triangular
(c) rectangular
(d) none of the above
Ans: c

69. A rectangular magnet of magnetic moment M is cut into two piece of same length, the magnetic moment of each piece will be
(a) M
(6) M/2
(c) 2 M
(d) M/4
Ans: b

70. A keeper is used to
(a) change the direction of magnetic lines
(b) amplify flux
(c)     restore lost flux
(d) provide a closed path for flux
Ans: d

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