Moving Charges and Magnetism Mock Test – Class 12 Physics

1. For oblique entry of a charged particle into a uniform magnetic field, the radius of the helical path is

2. A wire of length carries a current of perpendicular to a magnetic field of . The magnetic force on the wire is

3. A negative charge moves with velocity in a magnetic field . If points out of the page, the magnetic force on the charge points

4. Two identical long wires are perpendicular to the page and pass through points P and Q. The currents in both wires are out of the page. At the midpoint between P and Q, the magnetic fields due to the two wires are

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

6. 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

7. Assertion: If both and are reversed together for the same positive charge, the magnetic-force direction remains unchanged.
Reason: .

8. A rectangular loop lies in the plane of the page and carries clockwise current. A uniform magnetic field is directed to the right in the plane of the page. The magnetic forces on the upper and lower horizontal sides are

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

10. Study the table for the magnetic field at the centre of a circular coil.

The row containing an incorrect effect is

11. Two long parallel wires carry equal currents in opposite directions and are separated by . At the midpoint between them, the magnetic field magnitude is

12. A charged particle enters a magnetic field at to the field direction. If the speed is , the part of velocity responsible for magnetic force is

13. Reversing the current in a current loop changes the magnetic dipole moment because

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

15. A current-carrying wire of arbitrary shape is placed in a uniform magnetic field. Its endpoints are the same point because it forms a closed loop. The endpoint-displacement method predicts zero net force because

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

17. Study the table for a straight current-carrying conductor in a uniform magnetic field.

The row that contains an incorrect effect is

18. 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

19. A particle has charge , speed , and enters a magnetic field at . The magnitude of magnetic force is

20. A beam of charged particles enters a region where only a uniform magnetic field acts. The path bends, but the speed shown by the speed sensor remains constant. This happens because the magnetic force

21. 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

22. In the torque expression , the angle is measured between

23. A triangular current loop is placed in a uniform magnetic field. The three sides separately experience magnetic forces. The net magnetic force on the complete loop is

24. The magnetic field at the centre of a circular loop is . If the same length of wire is reshaped into a loop of half the radius by using two identical turns, with the same current in each turn, the new centre field is

25. In a moving-coil galvanometer, the soft iron core is used mainly to

26. A current element is directed along , and the observation point is located along from the element. The magnetic field contribution points along

27. Study the table and identify the only row in which both entries are properly matched.

28. A galvanometer of resistance is converted into a voltmeter by adding in series. If , the voltmeter range is

29. Assertion: If both the current direction and magnetic field direction are reversed for a straight conductor, the force direction remains unchanged.
Reason: Reversing both vectors in leaves the cross product unchanged.

30. A very long straight wire can be treated as the limiting case of a finite wire. If and in , the result becomes

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

32. A cyclotron has magnetic field and final orbit radius . A particle with and reaches the outer edge. Its maximum speed is

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

34. The magnetic field contribution due to a small current element is described by the Biot-Savart law. Its vector form is

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

36. If the separation between two long parallel wires is doubled while both currents remain unchanged, the force per unit length becomes

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

38. Magnetic field is best described as

39. A circular loop is viewed from the front, and the current appears anticlockwise. The magnetic field at the centre points

40. Use the graph description below.

The slope of the graph is

41. Assertion: In an ideal non-relativistic cyclotron, the time period of revolution is independent of the particle’s speed.
Reason: As the speed increases, the radius increases in the same proportion.

42. Use the graph description below.

If the slope of the graph is , and , the magnetic field magnitude is

43. For a charged particle in magnetic circular motion, the statement is constant but is not constant means that

44. Use the table for crossed electric and magnetic fields.

The row that contains a wrong crossed-field interpretation is

45. A circular Amperian loop encloses two long wires carrying currents out of the page and into the page. The value of in Ampere’s law, taking out of the page as positive, is

46. The magnetic force on a moving charge is zero in both parallel and anti-parallel motion because

47. Two long straight wires carry equal currents in opposite directions. The point of zero magnetic field is not between the wires because

48. A small current element and an observation point are arranged so that points toward the observation point. The Biot-Savart contribution at that point is

49. A positive ion passes undeflected through crossed electric and magnetic fields. If another ion with the same speed but negative charge enters along the same path, it can also pass undeflected because

50. Two long parallel wires P and Q are placed horizontally. P carries current to the right and Q carries current to the left. The magnetic interaction between them is