# 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

(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

(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