# Magnetic Fields and Forces

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Magnetic Fields and Forces
Chapter 24 Magnetic Fields and Forces Topics: Magnets and the magnetic field Electric currents create magnetic fields Magnetic fields of wires, loops, and solenoids Magnetic forces on charges and currents Magnets and magnetic materials Sample question: This image of a patient’s knee was made with magnetic fields, not x rays. How can we use magnetic fields to visualize the inside of the body? Slide 24-1

Key Points Three types of magnetic interactions
no interaction with either pole of a magnet => object is non-magnetic attracted to both poles of a magnet => object is magnetic Attracted to one pole and repelled by the other pole => object is a magnet Magnetic field vector from a bar magnet is a super position of the magnetic field vectors from the N and S poles: Vector from N pole points away from N pole Vector from S pole points towards S pole Field lines form complete loops inside and outside of magnet Field lines outside magnet go from N to S poles Field lines inside magnet go from S to N poles Magnetic Field vectors at a point are tangential to Magnetic Field Lines Answer: tesla

3-D Arrows, Cross Products, and Right Hand Rule 1
Showing vectors in 3D Cross Product For direction use Right-hand rule 1 Right-hand rule 1 (RHR 1) => for finding direction of cross-product vector (Cross-Product Rule) Point right hand in the direction of the first vector (vector A) Rotate your right hand until you can point your fingers in the direction of the second vector (vector B) Thumb points in direction the cross-product vector (vector C) Answer: tesla Slide 24-2

Electric vs. Magnetic Interactions
Nature of Magnetic Interactions Answer: tesla Slide 24-2

Discovering Magnetism
Slide 24-6

The Magnetic Field Slide 24-7

Mapping Out the Field of a Bar Magnet
Slide 24-8

Mapping Out the Magnetic Field Using Iron Filings
Slide 24-9

Drawing Field Lines of a Bar Magnet
Slide 24-10

Magnetic Fields Produced by Bar Magnets
A single bar magnet A single bar magnet (closeup) Slide 24-11

Magnetic Fields Produced by Bar Magnets
Two bar magnets, unlike poles facing Two bar magnets, like poles facing Slide 24-12

Checking Understanding
Slide 24-13

Magnetic Fields from Two Magnets
Bar Magnets A and B are placed at right angles. Two compasses, X and Y are placed so that they are equidistant from the two magnets as shown A.) The arrow in compass X indicates the direction in which the North pole of the compass is pointing. Indicate the North and South ends of both magnets in the diagram B.) Draw an arrow in compass Y to show the direction in which the North pole of the compass needle would point. Answer: tesla Slide 24-2

Magnetic Fields Around Us
Slide 24-14

Electric Currents Also Create Magnetic Fields
A long, straight wire A current loop A solenoid Slide 24-15

The Magnetic Field of a Straight Current-Carrying Wire
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Representing Vectors and Currents That Are Perpendicular to the Page
Slide 24-18

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 24-19

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? Answer: D Slide 24-20

Drawing Field Vectors and Field Lines of a Current-Carrying Wire
Slide 24-21

Drawing a Current Loop Slide 24-22

The Magnetic Field of a Current Loop
Slide 24-23

The Magnetic Field of a Solenoid
A short solenoid A long solenoid Slide 24-24

The Magnitude of the Field due to a Long, Straight, Current-Carrying Wire
Slide 24-25

Slide 24-26

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. 2.5 A to the left. Answer: E Slide 24-27

Answer The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire? 5 A to the left. Answer: E Slide 24-28