Electromagnetic Induction Mock Test – Class 12 Physics

1. A loop of area is shrinking in a uniform magnetic field directed into the page. The induced current is

2. A rectangular loop in a uniform magnetic field has an area-time graph described below.

For one turn, the magnitude of induced emf is

3. A plane loop is placed in a uniform magnetic field. The magnetic flux linked with it changes when

4. A pair of nearby coils is adjusted so that more magnetic flux produced by the primary links the secondary. The quantity that most directly increases is

5. A unit conversion record contains one correct relation for magnetic flux. Select it.

6. A flexible circular conducting loop is pulled into a larger circle while it remains perpendicular to a steady uniform magnetic field. The flux linked with the loop changes mainly because

7. Use the observations below from a magnet-coil experiment.

The row that conflicts with the usual observation is

8. Two coils are wound close together on a common soft iron core. Compared with the same coils far apart in air, their mutual inductance is usually

9. Assertion: If magnetic flux through a closed loop increases, the induced current acts so as to oppose that increase.
Reason: The negative sign in Faraday's law represents Lenz's law.

10. A secondary coil links of flux per turn when the primary current is . If the secondary has turns, the mutual inductance is

11. At the instant when the plane of a rotating coil is parallel to the magnetic field, the magnetic flux through the coil is

12. In a simple magnet-coil observation, the galvanometer deflects when the magnet is pushed toward the coil and deflects oppositely when the magnet is pulled away. What does the reversal mainly show?

13. Consider the following statements about mutual induction.
I. It needs changing magnetic flux linked with the secondary coil.
II. A soft magnetic core can increase coupling between the coils.
III. A perfectly steady primary current produces a continuing secondary emf after transients are over.

14. Consider the following statements about induced emf.
I. Its magnitude increases when the same flux change occurs in less time.
II. Its direction is decided by Lenz's law.
III. It can exist only after an induced current has already started flowing.

15. A rectangular coil has , , and rotates in a field . Its peak emf is . If the number of turns is increased to and the angular speed is reduced to of its earlier value while and are unchanged, the new peak emf is

16. A rectangular frame of area is placed in a uniform magnetic field of . The area vector of the frame is parallel to . What is the magnetic flux through the frame?

17. The sign of the induced emf in mutual induction is decided by

18. Two single-turn loops undergo the flux changes shown below.

The ratio of average emf magnitudes is

19. An induced current can flow in a circuit only when

20. Eddy current heating is useful in an induction furnace because

21. In the same primary-secondary coil arrangement, the galvanometer deflection on opening the key is opposite to that on closing the key. The reversal occurs because

22. A table lists transformer-related statements.

The faulty statement is

23. A rectangular coil rotates uniformly in a uniform magnetic field. The magnetic flux linked with it varies with time because

24. A rectangular surface has area and is placed perpendicular to a uniform magnetic field of . The magnetic flux through it is

25. Two loops lie in the plane of the page. In loop P, the magnetic field into the page is increasing. In loop Q, the magnetic field out of the page is increasing. The induced currents in P and Q are respectively

26. A circular loop of area lies in the plane of the page. The magnetic field into the page increases uniformly from to in . For a single turn, the magnitude of average induced emf is

27. A coil experiences the same rate of flux change in two trials. In Trial P, its resistance is ; in Trial Q, its resistance is . If the induced emf is the same in both trials, the current in Trial Q is

28. A circuit is placed in a magnetic field so that the flux linked with it changes uniformly. If the same total flux change is made in a shorter time, the induced emf magnitude becomes

29. A conducting loop is pulled out of a magnetic field region. The induced current produces a magnetic effect that resists the pull. The mechanical work done by the external agent is mainly converted into

30. A closed coil near a moving magnet has resistance . When induced current flows, the heat produced in the coil is best traced back to

31. In motional emf, a straight conductor moving through a magnetic field develops a potential difference mainly because

32. A rod of length moves perpendicular to a magnetic field with speed . If both and are doubled while is unchanged, the motional emf becomes

33. For a series circuit connected to a source, the current growth is governed by the time constant

34. A device needs strong mutual induction between two windings but small eddy current loss in the core. The most suitable choice is

35. Read the case below.

What should happen to the galvanometer deflection during the second motion?

36. Two coil pairs have the same primary current-change rate. Pair P has mutual inductance , while pair Q has mutual inductance . The ratio of secondary induced emf magnitudes is

37. A secondary coil of turns has flux through each turn changing uniformly by in . Its average induced emf magnitude is

38. A square loop of side is placed in a uniform magnetic field of . The plane of the loop is perpendicular to the field. The magnetic flux through the loop is

39. A square loop in a steady uniform magnetic field is compressed so that its area becomes half, while its area vector remains parallel to . The new magnetic flux is

40. The data for three sliding-rod circuits are shown below. Each rod moves perpendicular to the magnetic field.

The induced current magnitudes are

41. A rectangular loop is fully inside a uniform magnetic field region and is pulled with constant speed. The magnetic force opposing the motion becomes zero because

42. A loop lies in the plane of the page. The magnetic field through it is out of the page and decreasing. The induced current is

43. The self-induced emf in a coil of inductance is represented by

44. A compact way to state the magnitude part of Faraday's law is that induced emf depends on

45. The line resistance in a transmission system is . If the current is reduced from to by using a higher transmission voltage, the power loss changes from

46. A conducting plate has narrow slots cut in it before it is allowed to swing through a magnetic field. The plate experiences less damping because the slots

47. A pair of coaxial solenoids has , , common area , common length , and . Their mutual inductance is

48. A primary coil near a secondary coil is connected to a battery through a key. The secondary coil is connected to a galvanometer. Just after the key is closed, the galvanometer shows a momentary deflection because

49. In a secondary coil carrying mutually induced current, the heating of the coil wire is mainly due to

50. A comparison of two eddy-current situations is given below.

The row with the incorrect result is