1. Magnetic Fields and Forces
Chapter 24
Magnetic Fields and Forces

2. 24 Magnetic Fields and Forces
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3. Slide 24-3

4. Slide 24-4

5. Slide 24-5

6. Discovering Magnetism
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7. The Magnetic Field
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8. Mapping Out the Magnetic Field Using Iron Filings
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9. Mapping Out the Field of a Bar Magnet
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10. Drawing Field Lines of a Bar Magnet
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11. A single bar magnet (closeup)
Magnetic Fields Produced by Bar Magnets
A single bar magnet
A single bar magnet (closeup)
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12. Magnetic Fields Produced by Bar Magnets
Two bar magnets,
unlike poles facing
Two bar magnets,
like poles facing
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13. Checking Understanding
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14. Checking Understanding
Answer B A D E
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15. Magnetic Fields Around Us
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16. Electric Currents Also Create Magnetic Fields
A long, straight wire
A current loop
A solenoid
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17. The Magnetic Field of a Straight Current-Carrying Wire
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18. Slide 24-24

19. Representing Vectors and Currents That Are Perpendicular to the Page
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20. Checking Understanding
Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P?
Answer: D
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21. Answer
Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P? D.
Answer: D
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22. Drawing Field Vectors and Field Lines of a Current-Carrying Wire
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23. The Magnitude of the Field Due to a Long, Straight, Current-Carrying Wire
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24. Slide 24-30

25. Checking Understanding
The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire?
10 A to the right.
5 A to the right.
2.5 A to the right.
10 A to the left.
5 A to the left.
Answer: E
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26. Answer
The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire?
10 A to the right.
5 A to the right.
2.5 A to the right.
10 A to the left.
5 A to the left.
Answer: E
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27. Drawing a Current Loop
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28. The Magnetic Field of a Current Loop
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29. Checking Understanding
The diagram below shows a current loop perpendicular to the page; the view is a “slice” through the loop. The direction of the current in the wire at the top and the bottom is shown. What is the direction of the magnetic field at a point in the center of the loop?
To the left Up
To the right
Down
Answer: C
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30. Answer
The diagram below shows a current loop perpendicular to the page; the view is a “slice” through the loop. The direction of the current in the wire at the top and the bottom is shown. What is the direction of the magnetic field at a point in the center of the loop?
To the left Up
To the right
Down
Answer: C
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31. Checking Understanding
The diagram below shows slices through two adjacent current loops. Think about the force exerted on the loop on the right due to the loop on the left. The force on the right loop is directed
to the left.
up.
to the right.
down.
Answer: A
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32. Answer
The diagram below shows slices through two adjacent current loops. Think about the force exerted on the loop on the right due to the loop on the left. The force on the right loop is directed
to the left.
up.
to the right.
down.
Answer: A
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33. The Magnetic Field of a Solenoid
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34. Checking Understanding
What is the direction of the current in this solenoid, as viewed from the top?
Clockwise
Counterclockwise
Answer: B
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35. Answer
What is the direction of the current in this solenoid, as viewed from the top?
Clockwise
Counterclockwise
Answer: B
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36. The Magnetic Field of a Current Loop
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37. The Magnetic Field Inside a Solenoid
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38. Example Problems
A physics instructor is creating a demonstration that shows the direction of the field at the center of a current loop. He takes a cardboard form 25 cm in diameter and wraps 20 turns of wire around it in a tight loop. He wants the field at the loop’s center to be at least 10 times as large as the magnetic field of the earth, so that a compass will pivot convincingly to point in the direction of the field from the loop. How much current is needed to provide this field?
An investigator needs a uniform 30 mT field, which she intends to produce with a solenoid. She takes a long 10-cm-diameter tube and wraps wire along the length of it, wrapping 1200 turns of wire along a 75-cm length of the tube. How much current must she pass through the wire to produce the desired field?
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39. Example Problem
What is the direction and magnitude of the magnetic field at point P, at the center of the loop?
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40. The Force on a Charged Particle Moving in a Magnetic Field
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41. The Right-Hand Rule for Forces
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42. Slide 24-48

43. Paths of Charged Particles in Magnetic Fields
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44. The Mass Spectrometer
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45. Magnetic Fields Exert Forces on Currents
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46. Example Problem
A 10-cm length of wire carries a current of 3.0 A. The wire is in uniform field as in the diagram below. What is the magnitude and direction of the force on this segment of wire?
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47. Forces between Currents
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48. Slide 24-54

49. Forces between Current Loops
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50. A Current Loop Acts like a Bar Magnet
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51. Magnetic Fields Exert Torques on Current Loops
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52. The Torque on a Dipole in a Magnetic Field
  (IA)Bsin
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53. The Electric Motor
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54. Magnetic Resonance Imaging
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55. Magnetic Resonance Imaging
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56. Electron Magnetic Moments: Ferromagnetism
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57. Inducing a Magnetic Moment in a Piece of Iron
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58. Summary
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59. Summary
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60. Additional Questions
A loop carrying a current as shown rests in a uniform magnetic field directed to the right. If the loop is free to rotate,
it will rotate clockwise.
it will not rotate.
it will rotate counterclockwise.
Answer: C
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61. Answer
A loop carrying a current as shown rests in a uniform magnetic field directed to the right. If the loop is free to rotate,
it will rotate clockwise.
it will not rotate.
it will rotate counterclockwise.
Answer: C
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62. Additional Example
As ships move in the earth’s magnetic field, the field exerts a force on the charges in the metal body of the ship. Positive and negative charges feel a force in opposite directions, so a potential difference can result. A tanker is moving due west through the North Atlantic, where the earth’s field points nearly vertically downward. Is there a potential difference between the sides of the ship? If so, is the north side positive or negative?
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