magnetic circuit Mcqs
1. The rate of rise of current through an inductive coil is maximum_____________?
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A. at 63.2% of its maximum steady value

B. at the start of the current flow

C. after one time constant

D. near the final maximum value of current

2. If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be____________?
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A. large

B. small

C. zero

D. none of the above

3. A material for good magnetic memory should have____________?
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A. low hysteresis loss

B. high retentivity

C. low retentivity

D. high permeability

4. The unit of retentivity is____________?
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A. ampere turn/meter

B. weber/sq. m

C. ampere turn

D. weber

5. Hysteresis loss least depends on____________?
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A. steinmetz coefficient of material

B. ambient temperature

C. frequency

D. volume of material

6. An air gap is usually inserted in magnetic circuits to____________?
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A. prevent saturation

B. increase the flux

C. none of the above

D. increase m.m.f.

7. Laminated cores, in electrical machines, are used to reduce____________?
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A. all of the above

B. eddy current loss

C. hysteresis loss

D. copper loss

8. The unit of magnetic flux is______________?
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A. ampereturn/weber

B. ampere/metre

C. weber

D. henry

9. Conductance is analogous to_____________?
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A. reluctance

B. permeance

C. inductance

D. flux

10. When both the inductance and resistance of a coil are doubled the value of________________?
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A. time constant is halved

B. time constant remains unchanged

C. final steady current is doubled

D. initial rate of rise of current is doubled

11. Energy stored by a coil is doubled when its current is increased by percent___________?
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A. 41.4

B. 100

C. 50

D. 25

12. Relative permeability of vacuum is__________?
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A. 4n x 10- H/m

B. 1

C. 1/4JI

D. 1 H/m

13. In a magnetic material hysteresis loss takes place primarily due to___________?
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A. molecular friction

B. rapid reversals of its magnetisation

C. it high retentivity

D. flux density lagging behind magnetising force

14. Silicon steel is used in electrical machines because it has_____________?
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A. low coercivity

B. low retentivity

C. high coercivity

D. low hysteresis loss
15. The property of a material which opposes the creation of magnetic flux in it is known as_____________?
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A. reluctivity

B. permeance

C. reluctance

D. magnetomotive force

16. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is__________Vs
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A. 50

B. 20

C. 500

D. 0.05

17. Those magnetic materials are best suited for making armature and transformer cores which have ________ permeability and ________ hystersis loss
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A. low, low

B. low, high

C. high, low

D. high, high

18. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ?
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A. E.m.f.

B. Conductivity

C. Current density

D. Current
19. The relative permeability of a ferromagnetic material is_____________?
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A. more than 100 or 1000

B. less than one

C. more than 10

D. more than one

20. Those materials are well suited for making permanent magnets which have ________ retentivity and _________ coercivity
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A. high, high

B. low, low

C. low, high

D. high, low

21. The unit of reluctance is_____________?
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A. metre/henry

B. 1/henry

C. henry/metre

D. henry

22. Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it___________?
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A. produces fringing

B. leads to their increased weight

C. lowers their power efficiency

D. increases their cost of manufacture

23. Permeability in a magnetic circuit corresponds to________ in an electric circuit
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A. resistance

B. conductivity

C. resistivity

D. conductance

24. A ferrite core has less eddy current loss than an iron core because_______________?
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A. ferrites are magnetic

B. ferrites have high resistance

C. ferrites have high hysteresis

D. ferrites have low permeability

25. Hard steel is suitable for making permanent magnets because_____________?
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A. it has good residual magnetism

B. its mechanical strength is high

C. its hysteresis loop has large area

D. its mechanical strength is low

26. Conductivity is analogous to____________?
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A. resistivity

B. permeability

C. inductance

D. retentivity

27. Permanent magnets are normally made of_____________?
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A. alnico alloys

B. aluminium

C. wrought iron

D. cast iron

28. Reciprocal of reluctance is_______________?
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A. reluctivity

B. permeance

C. permeability

D. susceptibility