Magnetic Fields and Forces Chapter 24 Magnetic Fields and Forces

24 Magnetic Fields and Forces Slide 24-2

Slide 24-3

Slide 24-4

Slide 24-5

Discovering Magnetism Slide 24-12

The Magnetic Field Slide 24-13

Mapping Out the Magnetic Field Using Iron Filings Slide 24-14

Mapping Out the Field of a Bar Magnet Slide 24-15

Drawing Field Lines of a Bar Magnet Slide 24-16

A single bar magnet (closeup) Magnetic Fields Produced by Bar Magnets A single bar magnet A single bar magnet (closeup) Slide 24-17

Magnetic Fields Produced by Bar Magnets Two bar magnets, unlike poles facing Two bar magnets, like poles facing Slide 24-18

Checking Understanding Slide 24-19

Checking Understanding Answer B A D E Slide 24-20

Magnetic Fields Around Us Slide 24-21

Electric Currents Also Create Magnetic Fields A long, straight wire A current loop A solenoid Slide 24-22

The Magnetic Field of a Straight Current-Carrying Wire Slide 24-23

Slide 24-24

Representing Vectors and Currents That Are Perpendicular to the Page Slide 24-25

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 Slide 24-26

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 Slide 24-27

Drawing Field Vectors and Field Lines of a Current-Carrying Wire Slide 24-28

The Magnitude of the Field Due to a Long, Straight, Current-Carrying Wire Slide 24-29

Slide 24-30

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 Slide 24-31

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 Slide 24-32

Drawing a Current Loop Slide 24-33

The Magnetic Field of a Current Loop Slide 24-34

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 Slide 24-35

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 Slide 24-36

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 Slide 24-37

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 Slide 24-38

The Magnetic Field of a Solenoid Slide 24-39

Checking Understanding What is the direction of the current in this solenoid, as viewed from the top? Clockwise Counterclockwise Answer: B Slide 24-40

Answer What is the direction of the current in this solenoid, as viewed from the top? Clockwise Counterclockwise Answer: B Slide 24-41

The Magnetic Field of a Current Loop Slide 24-42

The Magnetic Field Inside a Solenoid Slide 24-43

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? Slide 24-44

Example Problem What is the direction and magnitude of the magnetic field at point P, at the center of the loop? Slide 24-45

The Force on a Charged Particle Moving in a Magnetic Field Slide 24-46

The Right-Hand Rule for Forces Slide 24-47

Slide 24-48

Paths of Charged Particles in Magnetic Fields Slide 24-49

The Mass Spectrometer Slide 24-50

Magnetic Fields Exert Forces on Currents Slide 24-51

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? Slide 24-52

Forces between Currents Slide 24-53

Slide 24-54

Forces between Current Loops Slide 24-55

A Current Loop Acts like a Bar Magnet Slide 24-56

Magnetic Fields Exert Torques on Current Loops Slide 24-57

The Torque on a Dipole in a Magnetic Field   (IA)Bsin Slide 24-58

The Electric Motor Slide 24-59

Magnetic Resonance Imaging Slide 24-60

Magnetic Resonance Imaging Slide 24-61

Electron Magnetic Moments: Ferromagnetism Slide 24-62

Inducing a Magnetic Moment in a Piece of Iron Slide 24-63

Summary Slide 24-64

Summary Slide 24-65

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 Slide 24-66

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 Slide 24-67

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? Slide 24-68