Moving Charges and Magnetism Mock Test – Class 12 Physics

1. 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

2. A cyclotron accelerates charged particles using

3. A long solenoid and a toroid both carry steady currents. A key difference between their ideal magnetic fields is that

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

5. A charged particle in a cyclotron has . If the cyclotron radius is doubled while , , and remain unchanged, the new maximum kinetic energy is

6. A student connects a galvanometer directly as an ammeter in a circuit where the current may be much larger than . The main problem is that

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

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

9. A toroid has turns and carries current . The magnetic field is required at a point inside the core at radius . Taking , the field is

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

11. Study the table and identify the row that gives the best magnetic-effect orientation.

Which row does not fit these magnetic-effect examples?

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

13. A long straight wire and a circular loop both carry current . At distance from the straight wire, , but far on the axis of the loop, . The difference arises mainly because

14. 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

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

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

17. The magnetic field on the axis of a single circular current loop of radius , at a distance from its centre, is

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

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

20. A particle of mass , charge magnitude , and speed moves perpendicular to a uniform magnetic field . Its centripetal acceleration is

21. In crossed fields, is upward and is into the page. A positive particle moves to the right. The electric force and magnetic force are respectively

22. Read the following case.

What is the instantaneous net force on the ion?

23. The starting idea behind magnetic effects of currents is that they are closely connected with ______.

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

25. 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

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

27. At a point on the axis of a circular current loop, the magnetic field is maximum when the point is

28. A current in wire P creates a magnetic field at the position of wire Q. Wire Q then experiences force because

29. A current loop behaves like a magnetic dipole in a uniform magnetic field. Its stable equilibrium occurs when

30. For a charged particle moving perpendicular to a uniform magnetic field, the radius of the circular path is

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

32. Study the table for motion of charged particles in a uniform magnetic field.

The row that gives an incorrect path is

33. Use the graph description below.

The slope of this graph is

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

35. Study the table about improving a moving-coil galvanometer.

The row with the incorrect effect is

36. The instantaneous power delivered by magnetic force on a moving charge is

37. Assertion: A current loop in a uniform magnetic field can have zero net force but non-zero torque.
Reason: Forces on opposite sides may cancel in translation while forming a couple.

38. In a right-hand-rule orientation for , the fingers are curled from toward . The thumb gives

39. A toroid has inner radius , outer radius , turns, and current . Taking , the magnetic field at inside the core is

40. The pitch of a helical path followed by a charged particle in a uniform magnetic field is

41. A charged particle enters a uniform magnetic field obliquely with fixed speed . If the angle with changes from to , the pitch changes by the factor

42. A galvanometer has coil resistance . Its voltage sensitivity is . Since , the voltage sensitivity is

43. A galvanometer is converted into a voltmeter using a high series resistance . If , the voltmeter resistance is approximately

44. 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.

45. 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

46. In an ideal toroid, the magnetic field outside the toroidal winding is approximately zero because an Amperian loop outside encloses

47. A loudspeaker is often mentioned with motors and galvanometers because its basic working also involves

48. Use the graph description below.

The slope of the graph represents

49. Use the graph description below.

The slope of this graph is

50. A charged particle enters a uniform magnetic field with and . Its time period in the circular part is . The pitch of the helical path is