41. Which point on the B-H curve in the above Fig. represents the average permeability ?
(i) point 5
(ii) point 2
(iii) point 1
(iv) point 4
Answer: (i) point 5
42. The hysteresis loop of a material having low retentivity is
(i) wide
(ii) narrow
(iii) very wide
(iv) none of above
Answer: (ii) narrow
43. The SI unit of µo is
(i) AT/m
(ii) Wb/m
(iii)Wb/AT-m
(iv) none of above
Answer: (iii)Wb/AT-m

44. The point 2 in the above Fig. represents
(i) residual flux density
(ii) coercive force
(iii) saturation flux density
(iv) none of above
Answer: (i) residual flux density
45. Which point in the above Fig. corresponds to coercive force ?
(i) point 1
(ii) point 5
(iii) point 2
(iv) point 6
Answer: (iv) point 6
46. The hysteresis loop shown in the above Fig. is for
(i) air
(ii) soft iron
(iii) steel
(iv) copper
Answer: (ii) soft iron
47. How would the loop in the above Fig. appear for a material with much less retentivity ?
(i) narrower
(ii) wider
(iii) no change
(iv) very wide
Answer: (i) narrower
48. The unit of relative permeability is
(i) AT/m
(ii) N/Wb
(iii) AT/m2
(iv) a number
Answer: (iv) a number
49. The hysteresis loss in a ferromagnetic material is
(i) directly proportional to area of loop
(ii) inversely proportional to area of loop
(iii) directly proportional to square of area of loop
(iv) none of above
Answer: (i) directly proportional to area of loop
50. At low frequencies, the material used for transformer cores is
(i) copper
(ii) silicon iron
(iii) soft iron
(iv) none of above
Answer: (ii) silicon iron
51. At high frequencies, the material used for transformer cores is
(i) silicon iron
(ii) soft iron
(iii) ferrite
(iv) none of above
Answer: (iii) ferrite
52. In practical magnetic circuits, the air-gap is kept
(i) very small
(ii) large
(iii) very large
(iv) none of above
Answer: (i) very small
53. The minimum relative permeability of a material can be
(i) 1
(ii) slightly less than 1
(iii) 0.005
(iv) none of above
Answer: (ii) slightly less than 1
54. In non-magnetic materials descending and ascending B-H curves
(i) coincide
(ii) do not coincide
(iii) sometime coincide and sometime not
(iv) none of above
Answer: (i) coincide
55. What is the magnetic field intensity in a material whose relative permeability is 1 when the flux density is 0.005 T ?
(i) 250 AT/m
(ii) 452 AT/m
(iii) 3980 AT/m
(iv) 1715 AT/m
Answer: (iii) 3980 AT/m
56. The relative permeability of air is
(i) 0
(ii) 1
(iii) infinite
(iv) none of above
Answer: (ii) 1
57. The slope of B-H curve of a material gives its
(i) absolute permeability
(ii) relative permeability
(iii) retentivity
(iv) none of above
Answer: (i) absolute permeability
58. The value of relative permeability of ferro-magnetic materials with increase in temperature
(i) increases
(ii) decreases
(iii) remains the same
(iv) none of above
Answer: (ii) decreases
59. A permanent magnet should have
(i) low remanence
(ii) high remanence
(iii) zero remanence
(iv) none of above
Answer: (ii) high remanence
60. An electromagnet uses
(i) soft iron core
(ii) steel core
(iii) nickel core
(iv) copper core
Answer: (i) soft iron core