MCQ Questions on Electromagnetism

1. The magnetic susceptibility of a paramagnetic material is

(a) less than zero
(b) less than one but positive
(c) greater than one
(d) equal to zero

2. Air exhibits

(a) ferromagnetism
(b) paramagnetism
(c) antiferromagnetism

3. Soft magnetic materials have

(a) high permeability and low coercive force
(b) low permeability and high coercive force
(c) high residual magnetism
(d) low resistivity

4. …….. is a soft magnetic material.

(A) Tungsten Steel
(B) Alcomax
(C) Bismuth
(D) Iron

5. Remanent magnetism is one which

(a) is left in the iron piece after the removal of the magnetic field
(b) is produced by the superconductor coils
(c) is produced by electric current
(d) is produced by induction

6. A bar magnet has

(a) monopole moment
(b) diapole moment
(c) both (a) and (b)
(d) none of these

7. Which of the following is a vector quantity

(a) magnetic potential
(b) susceptibility
(c) magnetic flux intensity
(d) magnetic flux density

8. The magnitude of force acting on a current carrying conductor placed in a magnetic field is independent of

(a) flux density
(b) length of conductor
(c) cross-sectional area of conductor
(d) current flowing through the conductor

9. If a current carrying conductor is placed in a magnetic field, the mechanical force experienced on the conductor is determined by

(a) simple product
(b) dot product
(c) cross product
(d) any of the above

10. The force experienced by a current carrying conductor lying parallel to a magnetic field is

(a) zero
(b) BIl
(c) BIl sin θ
(d) BIl cos θ

11. A magnetic field B and electric field E are perpendicular to each other as shown in figure given above. The path of electrons which starts at rest from origin O will be

(a) straight
(b) circular
(c) helical
(d) cycloidal

12. A coil wound over an iron ring carries certain current and establishes flux in the ring. If the area of x-section of the ring is doubled, the flux density in the core

(a) is doubled of the previous value
(b) is half of the previous value
(c) is same as the previous value
(d) is not possible to predict

13. The conductance of electrical circuit is analogous in magnetic circuit by

(a) flux
(b) reluctance
(c) permeance
(d) relative permeability

14. A cast steel electromagnet has an air gap length of 0.3 cm. Find the ampare-turns for the air gap to produce a flux density of 0.7 wb/m² in the gap.

(a) 2100 AT
(b) 1671 AT
(c) 1447 AT
(d) 167 AT

15. the magnetic field intensity (in A/m) at the centre of a circular coil of diameter 1 m and carrying a current of 2 A is

(a) 8
(b) 4
(c) 3
(d) 2

16. The field at any point on the axis of a current carrying coil will be

(a) perpendicular to the axis
(b) parallel to the axis
(c) at an angle of 45^o with the axis
(d) zero

17. An air gap is usually inserted in magnetic circuit so as to

(a) prevent saturation
(b) increase in MMF
(c) increase in flux
(d) increase in inductance

18. Which of the following statement is correct?

(a) the magnetic flux inside the exciting coil is the same as on its outer surface.
(b) the magnetic flux inside the exciting coil is zero.
(c) the magnetic flux inside the exciting coil is greater than that on its outer surface.
(d) the magnetic flux inside the exciting coil is lower than that on its outer surface.

19. If the two conductors carry current in opposite directions there will be

(a) a force of attraction between two conductors.
(b) a force of repulsion between two conductors.
(c) no force between them.
(d) none of the above

20. A straight conductor of circular x-section carries a current. Which one of the following statement is true in this regard?

(a) No force act on the conductor at any point.
(b) An axial force acts on the conductor tending to increase its length.
(c) A radial force acts towards the axis tending to reduce its cross-section.
(d) A radial force acts towards the axis tending to reduce its cross-section.

21. Consider the following statements:

The force per unit length between two stationary parallel wires carrying (steady) currents

1. is inversely proportional to the separation of wires.
2. is proportional to the magnitude of each current.
3. satisfies Newton’s third law.

Out of these statements
(a) 1 and 2 are correct.
(b) 2 and 3 are correct.
(c) 1 and 3 are correct.
(d) 1, 2 and 3 are correct.

22. Two parallel wires separated by a distance d are carrying a current I in the same direction. The magnetic field along a line running parallel to these wires and midway between them

(a) depends upon I
(b) is zero
(c) depends upon d
(d) depends upon the permeability of medium between the wires

23. linkage flux per unit current is called

(a) capacitance
(b) resistance
(c) inductance
(d) capacitive reactance

24. A magnetic circuit requires 800 at to produce a certain quantity of flux in a magnetic circuit. If its excitation coils has 100 turns and 5 ohm resistance, the voltage to be applied in exciting coils is

(a) 60 V
(b) 40 V
(c) 80 V
(d) 8 V

25. Which law is synonymous to the occurrence of diamagnetism?

(a) Ampere’s law
(b) Maxwell’s law
(c) Coulomb’s law
(d) Lenz’s law

26. If in an iron cored coil, the iron core is removed so as to make the air-cored coil, the inductance of the coil will be

(a) more
(b) less
(c) the same
(d) none of these

27. Lower the self inductance of a coil

(a) more will be the weber-turns
(b) more will be the EMF induced
(c) lesser the flux produced by it
(d) smaller the delay in establishing steady current through it

28. The unit(s) of inductance is/are

(a) Henry
(b) volt-second/A
(c) Wb/A
(d) all of the above

29. An open coil has

(a) zero resistance and zero inductance
(b) infinite resistance and infinite inductance
(c) infinite resistance and zero inductance
(d) zero resistance and infinite inductance

30. The inductance of a single layer solenoid of 10 turns is 5 micro µH. Which one of the following is the correct value of inductance when the number of turns is 20 and length is doubled?

(a) 10
(b) 20
(c) 40
(d) 5

31. Mutual inductance between two magnetically coupled coils depends on the

(a) permeability of the core material
(b) number of turns of the coil
(c) cross-sectional area of the coils
(d) cross-sectional area of their common core
(d) all of the above

32. Materials subjected to rapid reversals of magnetism should have

(a) high permeability and low hysteresis loss
(b) large B – H loop area
(c) large coercivity and retentivity
(d) low permeability and large coercivity

33. The magnetic field required to reduce the residual magnetism to zero is called

(a) retentivity
(b) coercivity
(c) hysteresis
(d) saturation magnetization

34. The coercive force in a ferromagnetic material is related to the

(a) area enclosed by the B – H loop
(b) intercept on the negative H axis of the B – H loop
(c) intercept on the positive B axis of the B – H loop
(d) maximum value of B on the B – H loop

35. Which of the following statements should be true if one compares the hysteresis loops of hard and soft magnetic materials?

1. Hysteresis loss of hard magnetic material will be less than that of soft material.
2. Coercivity of hard material will be greater than that of soft material.
3. Retentivity of two materials will always be equal.

Select the correct answer using the codes given below:
(a) 1 alone
(b) 2 alone
(c) 2 and 3
(d) 1, 2 and 3

36. The shape of B – H curve for air gap is

(a) parabola
(b) sinusoidal
(c) ellipse
(d) straight line

37. In a magnetic material, hysteresis loss takes place primarily due to

(a) flux density lagging behind magnetizing force
(b) molecular friction
(c) its high retentivity
(d) rapid reversal of its magnetization

38. Area of hysteresis loop is a measure of

(a) magnetic flux
(b) permeance
(c) MMF per cycle
(d) energy loss per cycle

39. Hysteresis loss least depends on

(a) volume of material
(b) frequency
(c) Steinmetz coefficient of material
(d) ambient temperature

40. The hysteresis is caused by

(a) structural non-homogeneity
(b) work required for magnetizing the material
(c) potential work function
(d) none of the above

41. Which of the following inductors will have the least eddy current losses?

(a) air-cored
(b) iron cored
(c) wooden cored
(d) laminated iron cored

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