# Magnets and the magnetic field - PowerPoint PPT Presentation

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## Magnets and the magnetic field

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### Chapter 24 Magnetic Fields and Forces Topics: Magnets and the magnetic field Electric currents create magnetic fields Magnetic fields of wires, loops, and solenoids – PowerPoint PPT presentation

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Title: Magnets and the magnetic field

1
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 patients 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
2
Magnetic Fields Around Us
Slide 24-14
3
Key Points
• Three types of magnetic interactions
• no interaction with either pole of a magnet gt
object is non-magnetic
• attracted to both poles of a magnet gt object is
magnetic
• Attracted to one pole and repelled by the other
pole gt 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

4
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.
Slide 24-2
5
Electric Currents Also Create Magnetic Fields
A long, straight wire
A current loop
A solenoid
Slide 24-15
6
Drawing Field Vectors and Field Lines of a
Current-Carrying Wire
Slide 24-21
7
The Magnitude of the Field due to a Long,
Straight, Current-Carrying Wire
Slide 24-25
8
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?
Slide 24-19
9
Point P is 5 cm above the wire as you look
straight down at it. In which direction is the
magnetic field at P?
Slide 24-20
10
The Magnetic Field of a Current Loop
Slide 24-23
11
The Magnetic Field of a Solenoid
A short solenoid
A long solenoid
Slide 24-24
12
Slide 24-26
13
Checking Understanding
The magnetic field at point P is zero. What are
the magnitude and direction of the current in the
lower wire?
1. 10 A to the right.
2. 5 A to the right.
3. 2.5 A to the right.
4. 10 A to the left.
5. 5 A to the left.
6. 2.5 A to the left.

Slide 24-27
14
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.

Slide 24-28
15
The Magnetic Field of a Current Loop
Slide 24-29
16
Example
What is the direction and magnitude of the
magnetic field at point P, at the center of the
loop?
Slide 24-30
17
The Magnetic Field Inside a Solenoid
Magnetic field inside a solenoid of length L with
N turns.
Slide 24-31
18
The Force on a Charged Particle Moving in a
Magnetic Field
Slide 24-32
19
The Right-Hand Rule for Forces
Slide 24-33
20
Slide 24-34
21
Paths of Charged Particles in Magnetic Fields
Slide 24-35
22
Magnetic Fields Exert Forces on Currents
Slide 24-37