Magnetic Circuits MCQ

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

42. The hysteresis loop of a material having low retentivity is

(i) wide
(ii) narrow
(iii) very wide
(iv) none of above

43. The SI unit of µ_o is

(i) AT/m
(ii) Wb/m
(iii)Wb/AT-m
(iv) none of above

44. The point 2 in the above Fig. represents

(i) residual flux density
(ii) coercive force
(iii) saturation flux density
(iv) none of above

45. Which point in the above Fig. corresponds to coercive force ?

(i) point 1
(ii) point 5
(iii) point 2
(iv) point 6

46. The hysteresis loop shown in the above Fig. is for

(i) air
(ii) soft iron
(iii) steel
(iv) copper

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

48. The unit of relative permeability is

(i) AT/m
(ii) N/Wb
(iii) AT/m²
(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

50. At low frequencies, the material used for transformer cores is

(i) copper
(ii) silicon iron
(iii) soft iron
(iv) none of above

51. At high frequencies, the material used for transformer cores is

(i) silicon iron
(ii) soft iron
(iii) ferrite
(iv) none of above

52. In practical  magnetic circuits, the air-gap is kept

(i) very small
(ii) large
(iii) very large
(iv) none of above

53. The minimum relative permeability of a material can be

(i) 1
(ii) slightly less than 1
(iii) 0.005
(iv) none of above

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

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

56. The relative permeability of air is

(i) 0
(ii) 1
(iii) infinite
(iv) none of above

57. The slope of B-H curve of a material gives its

(i) absolute permeability
(ii) relative permeability
(iii) retentivity
(iv) none of above

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

59. A permanent magnet should have

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

60. An electromagnet uses

(i) soft iron core
(ii) steel core
(iii) nickel core
 (iv) copper core