Magnetic Circuits MCQ

21. A magnetising force of 800 AT/m will produce a flux density of ………in air.

(i) 1 mWb/m²
(ii) 1 Wb/m²
(iii) 10 mWb/m²
(iv) 0.5 Wb/m²

22. The saturation flux density for most magnetic materials is about ……

(i) 0.5 Wb/m²
(ii) 10 Wb/m²
(iii) 2 Wb/m²
(iv) 1 Wb/m²

23. Hysteresis is the phenomenon ……… of in a magnetic circuit.

(i) lagging of B behind H
(ii) lagging of H behind B
(iii) setting up constant flux
(iv) none of the above

24. In the above Fig.the point ………. represents the saturation condition.

(i) b
(ii) c
(iii) a
(iv) e

25. In the above Fig. ………. represents the residual magnetism.

(i) of
(ii) oc
(iii) ob
(iv) none of the above

26. In the above Fig. oc represents the 

(i) residual magnetism
(ii) coercive force
(iii) retentivity
(iv) none of the above

27. If a magnetic material is located within a coil through which altenating current (50 Hz frequency) flows, then   ………… hysteresis loops will be formed every second.

(i) 50
(ii) 25
(iii) 100
(iv) 150

28. Out of the following materials, the area of hysteresis loop will be least for  ……..

(i) wrought iron
(ii) hard steel
(iii) silicon steel
(iv) soft iron

29. The materials used for ……….. the core of a good relay should have hysteresis loop.

(i) large
(ii) very large
(iii) narrow
(iv) none of the above

30. The magnetic material used for ………. should have a large hysteresis loop.

(i) transformers
(ii) d.c. generators
(iii) a.c. motors
(iv) permanent magnets

31. When transformer primary is fed from a.c., its core heats up due to 

(i) permeability of core
(ii) reluctance of core
(iii) ferromagnetism
(iv) hysteresis loss

32. Hysteresis loss can be reduced by 

(i) laminating the magnetic circuit
(ii) using material of narrow hysteresis loop
(iii) increasing m.m.f. of the circuit
(iv) none of the above

33. What is the mean magnetic length of the magnetic circuit shown in the above Fig.

(i) 1.2m
(ii) 2.4m
(iii) 0.24m
(iv) 0.8m

34. The magnetic flux density in the core in the above Fig. is

(i) 1 T
(ii) 0.5 T
(iii) 1.5 T
(iv) 0.8 T

35. If the magnetising force required at the working flux density in the above Fig. is 400 AT/m (form B-H curve), the required number of turn is

(i) 120
(ii) 240
(iii) 180
(iv) 320

36. The hysteresis loop for materials having high retentivity is

(i) wide
(ii) narrow
(iii) straight line passing through origin
(iv) data insufficient

37. Fringing effect is ignored in a magnetic circuit if air-gap is

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

38. An air-cored coil carries steady current. If air-core is replaced by a ferromagnetic material, the flux density in the core will

(i) remain same
(ii) decrease
(iii) increase
(iv) none of above

39. Another name for B-H curve in the above Fig. is

(i) magnetisation curve
(ii) permeability curve
(iii) shielding curve
(iv) none of above

40. Which point in B-H curve in the above Fig. is the saturation region ?

(i) point 5
(ii) point 2
(iii) point 1
(iv) point 4