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

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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

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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

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

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

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

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

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26. In the above Fig. oc represents the 

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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36. The hysteresis loop for materials having high retentivity is

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

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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

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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

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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

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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

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