Moving Charges and Magnetism Mock Test – Class 12 Physics

1. When the axial-field expression is used at the centre of the loop, the value of is

2. The magnetic dipole moment of an -turn current loop is written as

3. A cyclotron operating at high particle speeds becomes less effective when relativistic effects become significant because

4. A solenoid has turns in a length of and carries current . Taking , the magnetic field well inside the solenoid is

5. A circular loop of radius carries current . At a point on the axis, the magnetic field is half of the field at the centre. The axial distance satisfies

6. Study the table for a current element and an observation point at distance .

The row that contains an incorrect implication is

7. Use the graph description below.

The slope of this graph is

8. A charged particle moves through a magnetic field with speed . When the angle between and changes from to , with , , and unchanged, the magnetic force becomes

9. The magnetic field at the centre of a single circular loop of radius carrying current is

10. In the Ampere-law derivation of the magnetic field inside a long solenoid, a rectangular Amperian loop is chosen with one long side inside the solenoid and one long side outside. The outside contribution is neglected because

11. A particle of charge magnitude enters a uniform magnetic field with . The magnetic force can provide centripetal force because it is

12. A student claims that every force on a charge must be electric because charge is an electrical property. The claim misses the fact that

13. Study the table about maximum energy in a cyclotron.

The row with the incorrect dependence is

14. A closed conducting loop carrying steady current is placed completely in a uniform magnetic field. The net magnetic force on the loop is

15. A positively charged particle moving in a magnetic field has force magnitude . The force becomes maximum when

16. Consider the following statements about Ampere’s circuital law.
I. The path used in the line integral must be closed.
II. The current used is the algebraic net current enclosed by the path.
III. A zero value of always means everywhere on the path.
The correct set is

17. In crossed electric and magnetic fields, a charged particle moves without deflection. If the electric force and magnetic force are equal in magnitude and opposite in direction, the speed of the particle is

18. Study the table comparing meter conversions.

The row that is incorrect is

19. A circular coil and a long straight wire carry the same current . The field at the centre of a single circular loop of radius is compared with the field at distance from the long straight wire. The ratio is

20. A galvanometer of resistance is converted into an ammeter with shunt . If , the effective resistance of the ammeter is approximately

21. A galvanometer has current sensitivity and resistance . If the number of turns is increased, both and may increase. The voltage sensitivity will definitely improve only if

22. Use the graph description below.

The expected graph is

23. A galvanometer coil has , , , and . The current required for a deflection of is

24. Use the graph description below.

The graph is a straight line whose slope is

25. A galvanometer is converted into an ammeter of range . If is made larger while and remain the same, the required shunt resistance should

26. A current loop is compared with a bar magnet. The best statement is that the loop

27. Charged particles pass undeflected through crossed fields with and . They then enter a second uniform magnetic field perpendicular to their velocity. For a particle with , the radius in the second field is

28. A coil has torque when it carries current in a fixed magnetic field at a fixed orientation. If the number of turns and current are both doubled while , , and remain unchanged, the new torque is

29. A charged particle moving in a magnetic field has its velocity split as and relative to . If is doubled while , , , and remain unchanged, then

30. A proton and an alpha particle enter the same uniform magnetic field perpendicular to it with the same kinetic energy. Using , , , and , the ratio of their circular radii is

31. If the number of turns and magnetic field of a moving-coil galvanometer are both doubled while and remain unchanged, the current sensitivity becomes

32. Two long parallel wires carry currents and in the same direction. At the position of wire , the magnetic field due to wire is perpendicular to wire . The force per unit length on wire is obtained from

33. The SI unit of magnetic dipole moment of a current loop is

34. A high-resistance voltmeter is accidentally connected in series with a circuit branch. The branch current becomes very small mainly because

35. Study the table for two long parallel wires carrying currents and .

The row that contains an incorrect statement is

36. The maximum kinetic energy of a non-relativistic charged particle emerging from a cyclotron of radius is

37. A converted ammeter has appreciable resistance. When it is connected in series in a circuit, the measured current may be smaller than the original current because

38. The force per unit length between two long parallel wires separated by distance , carrying currents and , is

39. For a small element of a current-carrying wire placed in a magnetic field, the magnetic force on that element is written as

40. For the same charged particle moving in the same magnetic field, Case 1 has and Case 2 has . The ratio of magnetic force magnitudes is

41. A galvanometer has resistance and gives full-scale deflection for . It is to be converted into an ammeter of range . The required shunt resistance is approximately

42. A positive charge moves along the positive -axis and enters a uniform magnetic field along the positive -axis. The direction of magnetic force on the charge is

43. A charge is momentarily at rest in a region where and . The Lorentz force at that instant is

44. A voltmeter made from a galvanometer has range and total resistance . The full-scale galvanometer current is

45. A current element produces at a point. If the current is doubled and the distance of the point from the element is also doubled, with and unchanged, the new magnetic field contribution is

46. A closed path is chosen near a long straight wire, but the wire lies outside the closed path. For that path, Ampere’s law gives

47. At the centre of a circular current loop carrying current , the magnetic field is directed

48. A moving-coil galvanometer is made more sensitive by decreasing the torsional constant . A possible limitation is that

49. If the magnetic field of a cyclotron is doubled while the particle species remains the same, the required oscillator frequency should

50. A finite wire result is used for a point near one end of a semi-infinite straight wire. If the angles are and , the field is