Chapter 28: Magnetic Induction

1. Chapter 28: Magnetic Induction Section 28-1: Magnetic Flux

2. A square loop of sides a lies in the yz plane with one corner at the origin. A varying magnetic field B = ky passes through the loop and points in the +x direction. The magnetic flux through the loop is • ka2 • ka2/2 • ka3/2 • ka3/3 • None of these is correct.

3. A square loop of sides a lies in the yz plane with one corner at the origin. A varying magnetic field B = ky passes through the loop and points in the +x direction. The magnetic flux through the loop is • ka2 • ka2/2 • ka3/2 • ka3/3 • None of these is correct.

4. You can change the magnetic flux through a given surface by • changing the magnetic field. • changing the surface area over which the magnetic field is distributed. • changing the angle between the magnetic field and surface in question. • any combination of a through c. • none of these strategies.

5. You can change the magnetic flux through a given surface by • changing the magnetic field. • changing the surface area over which the magnetic field is distributed. • changing the angle between the magnetic field and surface in question. • any combination of a through c. • none of these strategies.

6. Suppose you double the magnetic field in a given region and quadruple the area through which this magnetic field exists. The effect on the flux through this area would be to • leave it unchanged. • double it. • quadruple it. • increase it by a factor of six. • increase it by a factor of eight.

7. Suppose you double the magnetic field in a given region and quadruple the area through which this magnetic field exists. The effect on the flux through this area would be to • leave it unchanged. • double it. • quadruple it. • increase it by a factor of six. • increase it by a factor of eight.

8. The magnetic flux through a loop is made to vary according to the relationwhere the units are SI. The emf induced in the loop when t = 2 s is • 38 V • 39 V • 40 V • 31 V • 19 V

9. The magnetic flux through a loop is made to vary according to the relationwhere the units are SI. The emf induced in the loop when t = 2 s is • 38 V • 39 V • 40 V • 31 V • 19 V

10. The magnetic flux through a certain coil is given bywhere the units are SI. The coil has 100 turns. The magnitude of the induced emf when t = 1/200 s is • 100 V • 200 V • zero • 2/pi V • 1/50pi V

11. The magnetic flux through a certain coil is given bywhere the units are SI. The coil has 100 turns. The magnitude of the induced emf when t = 1/200 s is • 100 V • 200 V • zero • 2/pi V • 1/50pi V

12. For which of the diagram(s) will current flow through the light bulb? (In 3 and 4 assume the magnets move in the plane of the loop.) • 1 • 2 • 3 • 4 • 1 and 2

13. For which of the diagram(s) will current flow through the light bulb? (In 3 and 4 assume the magnets move in the plane of the loop.) • 1 • 2 • 3 • 4 • 1 and 2

14. A circular loop of radius R has 50 turns. It lies in the xy plane. A time dependent magnetic field B(t) = A sin (ωt) where A is a constant, passes through the loop in the +z direction. The emf induced in the loop is • 50πAR2 sin (ωt) • 50πAR2 cos (ωt) • 50πωAR2 sin (ωt) • 50πωAR2 cos (ωt) • None of these is correct.

15. A circular loop of radius R has 50 turns. It lies in the xy plane. A time dependent magnetic field B(t) = A sin (ωt) where A is a constant, passes through the loop in the +z direction. The emf induced in the loop is • 50πAR2 sin (ωt) • 50πAR2 cos (ωt) • 50πωAR2 sin (ωt) • 50πωAR2 cos (ωt) • None of these is correct.

16. Chapter 28: Magnetic Induction Section 28-2: Induced EMF and Faraday’s Law

17. The plane of a circular, 200-turn coil of radius 5.25 cm is perpendicular to a uniform magnetic field produced by a large electromagnet. This field is changed at a steady rate from 0.650 T to 0.150 T in 0.0100 s. What is the magnitude of the emf induced in the coil? • 110 V • 170 V • 1.7 V • 26 V • 87 V

18. The plane of a circular, 200-turn coil of radius 5.25 cm is perpendicular to a uniform magnetic field produced by a large electromagnet. This field is changed at a steady rate from 0.650 T to 0.150 T in 0.0100 s. What is the magnitude of the emf induced in the coil? • 110 V • 170 V • 1.7 V • 26 V • 87 V

19. According to Faraday's law, a necessary and sufficient condition for an electromotive force to be induced in a closed circuit loop is the presence in the loop of • a magnetic field. • magnetic materials. • an electric current. • a time-varying magnetic flux. • a time-varying magnetic field.

20. According to Faraday's law, a necessary and sufficient condition for an electromotive force to be induced in a closed circuit loop is the presence in the loop of • a magnetic field. • magnetic materials. • an electric current. • a time-varying magnetic flux. • a time-varying magnetic field.

21. The instantaneous induced emf in a coil of wire located in a magnetic field • depends on the time rate of change of flux through the coil. • depends on the instantaneous value of flux through the coil. • is independent of the area of the coil. • is independent of the number of turns of the coil. • is determined by the resistance in series with the coil.

22. The instantaneous induced emf in a coil of wire located in a magnetic field • depends on the time rate of change of flux through the coil. • depends on the instantaneous value of flux through the coil. • is independent of the area of the coil. • is independent of the number of turns of the coil. • is determined by the resistance in series with the coil.

23. Chapter 28: Magnetic Induction Section 28-3: Lenz’s Law and Concept Check 28-1

24. Using the alternative statement of Lenz’s law, find the direction of the induced current in the loop shown if the magnet is moving to the left (away from the loop). • Clockwise. • Counterclockwise. • No current is induced.

25. Using the alternative statement of Lenz’s law, find the direction of the induced current in the loop shown if the magnet is moving to the left (away from the loop). • Clockwise. • Counterclockwise. • No current is induced.

26. A copper ring lies in the yz plane as shown. The magnet's long axis lies along the x axis. Induced current flows through the ring as indicated. The magnet • must be moving away from the ring. • must be moving toward the ring. • must remain stationary to keep the current flowing.

27. A copper ring lies in the yz plane as shown. The magnet's long axis lies along the x axis. Induced current flows through the ring as indicated. The magnet • must be moving away from the ring. • must be moving toward the ring. • must remain stationary to keep the current flowing.

28. A conducting loop around a bar magnet begins to move away from the magnet. Which of the following statements is true? • The magnet and the loop repel one another. • The magnet and the loop attract one another. • The magnet and loop neither attract nor repel one another.

29. A conducting loop around a bar magnet begins to move away from the magnet. Which of the following statements is true? • The magnet and the loop repel one another. • The magnet and the loop attract one another. • The magnet and loop neither attract nor repel one another.

30. A loop rests in the xy plane. The z axis is normal to the plane and positive upward. The direction of the changing flux is indicated by the arrow along the z axis. Which diagram correctly shows the direction of the resultant induced current in the loop?

31. A loop rests in the xy plane. The z axis is normal to the plane and positive upward. The direction of the changing flux is indicated by the arrow along the z axis. Which diagram correctly shows the direction of the resultant induced current in the loop?

32. For which of the following diagrams will current flow in the clockwise direction? • 1 and 2 • 3 and 4 • 1 and 3 • 2 and 4 • 2 and 3

33. For which of the following diagrams will current flow in the clockwise direction? • 1 and 2 • 3 and 4 • 1 and 3 • 2 and 4 • 2 and 3

34. A bar magnet is dropped through a loop of copper wire as shown. Recall that magnetic field lines point away from a north pole and toward a south pole. If the positive direction of the induced current I in the loop is as shown by the arrows on the loop, the variation of I with time as the bar magnet falls through the loop is illustrated qualitatively by which of the graphs? The time when the midpoint of the magnet passes through the loop is indicated by C.

35. A bar magnet is dropped through a loop of copper wire as shown. Recall that magnetic field lines point away from a north pole and toward a south pole. If the positive direction of the induced current I in the loop is as shown by the arrows on the loop, the variation of I with time as the bar magnet falls through the loop is illustrated qualitatively by which of the graphs? The time when the midpoint of the magnet passes through the loop is indicated by C.

36. Which law does the following statement express? "In all cases of electromagnetic induction, the induced voltages have a direction such that the currents they produce oppose the effect that produces them." • Maxwell's law • Fleming's rule • Lenz's law • Gauss's law • Ampère's law

37. Which law does the following statement express? "In all cases of electromagnetic induction, the induced voltages have a direction such that the currents they produce oppose the effect that produces them." • Maxwell's law • Fleming's rule • Lenz's law • Gauss's law • Ampère's law

38. Chapter 28: Magnetic Induction Section 28-4: Motional EMF and Concept Check 28-2

39. When a generator delivers electric energy to a circuit, where does the energy come from? • The energy comes from an external source of electrical power, such as a battery or electrical outlet. • The energy comes from the heat being absorbed by the coil as it turns. • The energy comes from an external agent, which is doing mechanical work on the coil. • The energy comes from chemical reactions within the coil. • The energy comes from nuclear reactions within the coil.

40. When a generator delivers electric energy to a circuit, where does the energy come from? • The energy comes from an external source of electrical power, such as a battery or electrical outlet. • The energy comes from the heat being absorbed by the coil as it turns. • The energy comes from an external agent, which is doing mechanical work on the coil. • The energy comes from chemical reactions within the coil. • The energy comes from nuclear reactions within the coil.

41. A wire rod rolls with a speed of 20 m/s on two metallic rails, 1.0 m apart, that form a closed loop. If the magnetic field is 1.5 T into the page, the power dissipated in the resistor R and the current direction are, respectively, • 33 mW, clockwise. • 33 mW, counterclockwise. • 76 mW, counterclockwise. • 76 mW, clockwise. • 50 mW, clockwise.

42. A wire rod rolls with a speed of 20 m/s on two metallic rails, 1.0 m apart, that form a closed loop. If the magnetic field is 1.5 T into the page, the power dissipated in the resistor R and the current direction are, respectively, • 33 mW, clockwise. • 33 mW, counterclockwise. • 76 mW, counterclockwise. • 76 mW, clockwise. • 50 mW, clockwise.

43. A wire rod rolls with a speed of 30 m/s on two metallic rails, 2.0 m apart, that form a closed loop. The power dissipated in the resistor R and the current direction are, respectively, • 33 mW, clockwise. • 33 mW, counterclockwise. • 2.0 W, counterclockwise. • 10 W, clockwise. • 10 W, counterclockwise.

44. A wire rod rolls with a speed of 30 m/s on two metallic rails, 2.0 m apart, that form a closed loop. The power dissipated in the resistor R and the current direction are, respectively, • 33 mW, clockwise. • 33 mW, counterclockwise. • 2.0 W, counterclockwise. • 10 W, clockwise. • 10 W, counterclockwise.

45. A wire rod rolls with a speed of 8.0 m/s on two metallic rails, 30 cm apart, that form a closed loop. A uniform magnetic field of magnitude 1.20 T is into the page. The magnitude and direction of the current induced in the resistor R are • 0.82 A, clockwise. • 0.82 A, counterclockwise. • 1.2 A, clockwise. • 1.2 A, counterclockwise. • 2.9 A, counterclockwise.

46. A wire rod rolls with a speed of 8.0 m/s on two metallic rails, 30 cm apart, that form a closed loop. A uniform magnetic field of magnitude 1.20 T is into the page. The magnitude and direction of the current induced in the resistor R are • 0.82 A, clockwise. • 0.82 A, counterclockwise. • 1.2 A, clockwise. • 1.2 A, counterclockwise. • 2.9 A, counterclockwise.

47. A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is entering the field, which arrow shows the direction of the magnetic force?

48. A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is entering the field, which arrow shows the direction of the magnetic force?

49. A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is exiting the field on the right, which arrow shows the direction of the magnetic force?

50. A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is exiting the field on the right, which arrow shows the direction of the magnetic force?