Moving Charges and Magnetism Mock Test – Class 12 Physics

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

2. A long straight wire carries current out of the page. The magnetic field at a point above the wire on the page is directed

3. 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

4. A magnetic dipole is slightly displaced from its stable equilibrium in a uniform magnetic field. The torque that appears tends to

5. The potential energy of a magnetic dipole in a uniform magnetic field is

6. A long straight wire carries current into the page. The magnetic field pattern on the page is

7. A square loop of side carries current and is placed in a uniform magnetic field. If the field lies in the plane of the loop and is parallel to one pair of opposite sides, then the force on those parallel sides is

8. For a non-relativistic charged particle in a cyclotron, the cyclotron frequency is

9. A region has crossed fields of magnitudes and . The speed for undeflected motion is

10. Read the following passage.

Particles emerging undeflected from the region have

11. Study the table for a charged particle moving with the same speed in the same magnetic field.

The row that contains an incorrect force condition is

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

13. A current loop has area vector , current , and magnetic moment . The relation for an -turn loop indicates that the unit of magnetic moment is

14. A beam enters a velocity selector. Particles with speed lower than deflect toward the electric-force side. This happens because

15. A galvanometer is converted into an ammeter by a shunt. If the shunt resistance is accidentally made larger than the calculated value, then for the same total current

16. Two particles have the same charge magnitude and enter the same magnetic field perpendicular to it with equal speeds. Particle P has mass , and particle Q has mass . If their kinetic energies are not separately specified, the ratio of radii is

17. A charged particle moving perpendicular to a uniform magnetic field has kinetic energy and path radius . If its kinetic energy becomes while , , and remain unchanged, the new radius is

18. A rectangular coil in a radial magnetic field has , , , and . The deflection produced by current is

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

20. A rectangular current loop is arranged so that the plane of the loop is parallel to a uniform magnetic field. The area vector of the loop is then perpendicular to , so the torque is

21. In a moving-coil galvanometer, a radial magnetic field is used so that

22. A converted voltmeter has too low a resistance compared with the circuit element across which it is connected. The likely effect is that it

23. A force sensor compares two long parallel-wire setups. Setup P has currents and separated by . Setup Q has currents and separated by . The ratio is

24. Assertion: Two magnetic field lines cannot intersect each other.
Reason: At a single point, cannot have two different directions simultaneously.

25. A charged particle moves in a region where both electric field and magnetic field are present. The total force on the particle is represented by

26. A straight current-carrying wire is perpendicular to a uniform magnetic field. If the current direction alone is reversed while , , and remain unchanged, the force on the wire

27. Use the graph description below.

The graph is symmetric about because

28. A particle moving perpendicular to a uniform magnetic field has radius . If the magnetic field is doubled while speed, mass, and charge magnitude are unchanged, the new radius is

29. The magnetic field outside a very long ideal solenoid is treated as approximately

30. A moving charged particle is observed to pass through a magnetic field without any magnetic deflection. One possible reason is that

31. Ampere’s law gives the field of a long straight wire as . The factor enters the derivation as

32. At any point on a magnetic field line, the direction of is given by

33. Two points P and Q are at distances and from a long straight wire carrying current . The ratio is

34. A charged particle moves perpendicular to a magnetic field in a circle of radius . If its charge magnitude is doubled and its kinetic energy is also doubled while and are unchanged, the new radius is

35. Consider the following examples:
I. Deflection of a compass near a current-carrying wire
II. Rotation of the coil in an electric motor
III. Change in weight of a body on a balance
IV. Deflection in a moving-coil galvanometer
The examples most directly connected with magnetic effects of currents are

36. A cyclotron is generally unsuitable for accelerating electrons to high energy using the simple resonance condition mainly because electrons

37. A particle with mass and charge magnitude moves perpendicular to a uniform magnetic field of . Its angular frequency is

38. A galvanometer has , , , and torsional constant . Its current sensitivity is

39. For a fixed current element and fixed angle , the Biot-Savart law predicts that varies with distance as

40. Consider two statements about a magnetic dipole in a uniform magnetic field.
I. At , the dipole has minimum potential energy.
II. At , the torque magnitude is maximum.
The best evaluation is

41. A graph of magnetic field against distance for a long straight wire is not a straight line. A straight-line graph can be obtained by plotting against

42. A charged particle enters a region containing only a uniform magnetic field. After some time, the direction of its velocity has changed but its speed is unchanged. This observation is best explained because the magnetic force

43. The torque on a magnetic dipole moment in a uniform magnetic field is represented by

44. Two long parallel wires are apart and carry currents and in the same direction. Taking , the force per unit length between them is

45. A galvanometer gives full-scale deflection for current and has resistance . To convert it into an ammeter of range , where , a shunt resistance is connected

46. A particle passes through crossed fields undeflected and then enters a region containing only a magnetic field. The first region selects speed, while the second region bends the path. This sequence is useful because

47. For a moving-coil galvanometer in radial magnetic field, the equilibrium condition is

48. A galvanometer is converted into a voltmeter of range . If the required range is increased from to , while and remain unchanged, the added series resistance changes from to

49. A long straight wire carries current . The magnetic field at a point from the wire is approximately .

50. A converted voltmeter has resistance and is connected across a resistor in a circuit. The measured branch resistance becomes