Magnetic Circuits MCQ

61. Magnetic shields are made from materials having

(i) low permeability
(ii) high permeability
(iii) zero permeability
(iv) none of above

62. The hysteresis cycle for the material of a transformer is

(i) tall and narrow
(ii) tall and wide
(iii) short and narrow
(iv) short and wide

63. The current in the winding shown in the above Fig. is 3.2 A. If the winding has 60 turns, the magnetic field intensity in the core is

(i) 242.2 AT/m
(ii) 417.4 AT/m
(iii) 332.8 AT/m
(iv) 141.4 AT/m

64. The ohm’s law for magnetic circuit is

(i) reluctance =  flux/m. m. f.
(ii) m.m.f = reluctance/flux
(iii) m.m.f. = flux/reluctance
(iv) m.m.f. = flux x reluctance

65. The curie temperature of iron is

(i) 200°C
(ii) 430°C
(iii) 770°C
(iv) 550°C

66. Ferromagnetic materials exhibit hysteresis when

(i) they are taken to saturation only
(ii) they are not taken even to saturation
(iii) they are heated to very high temperature
(iv) none of above

67. A permanent magnet should have

(i) high coercivity
(ii) low coercivity
(iii) zero coercivity
(iv) none of above

68. The B-H curve of a ferromagnetic material is

(i) linear
(ii) non-linear
(iii) circle
(iv) none of above

69. Magnetic materials that have high retentivity have a

(i) narrow hysteresis loop
(ii) circular hysteresis loop
(iii) nearly square hysteresis loop
(iv) none of above

70. The hysteresis loop of the core material of a transformer should have

(i) a large area
(ii) a small area
(iii) an infinite area
(iv) none of above

71. The magnetic intensity in the air core of the solenoid shown in the above Fig. is changed by 20 AT/m. By what amount the flux density in the core is changed ?

(i) 2 x 10^-6 T
(ii) 1 T
(iii) 3.58 x 10^-4 T
(iv) 2.51 x 10^-5 T

72. In an electromagnet, the flux density at saturation should be

(i) high
(ii) low
(iii) zero
(iv) none of above