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## Magnetism

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### Chapter 21 James Clerk Maxwell Michael Faraday What is magnetism? a phenomena in which certain materials exert attractive/repulsive forces on other materials. – PowerPoint PPT presentation

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Title: Magnetism

1
Magnetism
Chapter 21
James Clerk Maxwell
2
What is magnetism?
• a phenomena in which certain materials exert
attractive/repulsive forces on other materials.
• These materials contain a region where these
forces can be detected. (Magnetic fields)

3
Where do magnetic fields occur?
4
Where do magnetic fields occur?
5
How do Magnetic fields work?
Field lines move away from the north pole.
Field lines move towards the south pole.
6
Magnetic Field of the Earth
• North magnetic pole located at south geographic
pole.
• South magnetic pole located at north geographic
pole.

7
Magnetic Field Strength
• The strength of a magnetic field (B) is related
to the amount of magnetic force (F) that is
applied to a moving test charge when it is at a
given location in the field.

B Fmagnetic q?
q test charge magnitude ? speed of the charge
8
Sample Problem
• A proton moving east experiences an upward force
of
• 8.8 x 10-19 N due to the Earths magnetic field.
The field has
• a strength of 5.5 x 10-5 Teslas (T) to the
north. Find the
• speed of the proton.

B Fmagnetic q?
q 1.60 x 10-19 C
B 5.5 x 10-5 T
? Fmagnetic qB
Fmagnetic 8.8 x 10-19 N
? 8.8 x 10-19 N _
(1.60 x 10-19 C) (5.5 x 10-5 T)
1.0 x 105 m/s
9
Direction of magnetic force
• The direction of the magnetic force is
perpendicular to the plane of the magnetic field
and to the direction of the charge.
• USE RIGHT HAND RULE!!!

10
Magnetic force in current-carrying wires
• Current carrying wires that are placed in a
magnetic field also experience a magnetic force.

11
Magnetic force in current-carrying wires
• The magnitude of the magnetic force can be
written in terms of the current (I) flowing
through the length of the wire (L).

F BIL
12
Sample Problem
• A 10.0 m long powerline carries a current of 20.0
A
• perpendicular to the Earths magnetic field of
• 5.5 x 10-5 T. What is the magnetic force
experienced
• by the power line?

I 20.0 A
B 5.5 x 10-5 T
F BIL
L 10.0 m
F (5.5 x 10-5 T)(20.0 A)(10.0 m)
0.011 N
13
Magnetic fields from electricity
• Charges that are in motion (an electrical
current) produce magnetic fields.

Magnetic field moves around a wire with a current
in a circular fashion. Which direction???
14
Right Hand Rule
• Thumb goes in the direction of the current.
• 2. Fingers wrap around wire in the direction of
the magnetic field.

15
Electromagnets
• Arranging wire in a coil and running a current
through produces a magnetic field that is similar
to a bar magnet.

16
Electromagnetic Induction
It is possible to induce an electric current
without the use of a battery or power supply.
Coil Solenoid
17
Electromagnetic Induction
Produces an electromotive force (emf)
18
Lenzs Law
An electromagnetic field interacting with a
conductor will generate electrical current that
induces a counter magnetic field that opposes the
magnetic field generating the current.