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Journal 4/10/17
If you heat up a magnet to a high temperature, it can
lose its magnetic property and become just a lump of
metal. Use what you’ve learned so far to explain why.
Objective
To learn about the forces
created by magnetic fields
Tonight’s Homework
pp 499: 5, 6, 7
Notes on Magnetism from Current
How are magnetism and electricity
related? L ‘Oersted found that if he
brought an electric wire near a magnet
(compass), the magnet would deflect.
Notes on Magnetism from Current
How are magnetism and electricity
related? L ‘Oersted found that if he
brought an electric wire near a magnet
(compass), the magnet would deflect.
It seems that moving electricity – or
electric current – induces a magnetic
field!
Notes on Magnetism from Current
A straight wire is the simplest setup we
can create.
The magnetic field goes
around the wire
perpendicular to it.
Notes on Magnetism from Current
A straight wire is the simplest setup we
can create.
The magnetic field goes
around the wire
perpendicular to it.
The farther we get from
the wire, the weaker the field gets.
There’s a trick to remembering which way
the field goes.
Notes on Magnetism from Current
This is called the right hand rule.
If you point your thumb along the wire,
your fingers will curl in the direction of
the magnetic field.
Notes on Magnetism from Current
If electricity can create magnetic field
lines, it can turn ferromagnets into
magnets as long as a current is running
through it.
Notes on Magnetism from Current
If electricity can create magnetic field
lines, it can turn ferromagnets into
magnets as long as a current is running
through it.
We call this an electromagnet. It can be
turned on and off at will. We’ll go into
more depth on this later!
Notes on Magnetism from Current
If we shoot a charged particle into a
magnetic field it will be deflected. For an
electron, we can use the relationship
shown here:
Notes on Magnetism from Current
If we shoot a charged particle into a
magnetic field it will be deflected. For an
electron, we can use the relationship
shown here:
“Current” is the
direction the electron
is moving.
“Force” is the direction the electron will
be bent.
This is usually called the “FBI” rule.
Notes on Magnetism from Current
For positively charged particles, just use
your left hand instead of your right.
Notes on Magnetism from Current
Imagine we place a wire in a magnetic
field. This has a whole stream of charged
particles and will be bent as well.
Notes on Magnetism from Current
Imagine we place a wire in a magnetic
field. This has a whole stream of charged
particles and will be bent as well.
Our FBI rule works to predict this as well.
Equations
Force on a
wire from
magnetism
E
F = BIL
V
F: Force in Newtons
B: Magnetic field strength in Telsa
I: Current through the wire in Amps
L: Length of the wire in the field in m.
S
This equation tells up how much force
will bend a wire with current if that
wire passes through a magnetic field.
To find the direction that it will bend,
use the FBI rule.
Magnetism from Current Review
Two magnets are shown below. Which situation best shows how the
magnetic field lines will look?
SETUP
C
A
D
B
E
Magnetism from Current Review
The core of the Earth acts like one giant magnet. So why does a
common refrigerator magnet measure a much higher strength of
magnetic field in Teslas?
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A) Because you’re farther from Earth’s core than a common magnet.
B) Because the Earth’s magnetic field is spread over a whole planet.
C) The materials in a refrigerator magnet can generate magnetism
more efficiently than those in the center of the Earth.
D) All of the above
E) None of the above
Magnetism from Current Review
A “dip needle” is like a compass, but moves up and down instead of
side to side. At what location would you need to stand on the Earth to
get the dip needle pointing straight down?
A
B
C
D
E
Magnetism from Current Review
We have a particle in a magnetic field as shown, moving
down. Which diagram best shows which way the electron
will move next?
x
x
x
x
x
x
x
x
x
x
x
Bx
x
x
x
x
x
x
e
SETUP
x
e
e
x
A
B
it won’t move
e
e
C
D
e
E
Exit Question
Which of the following would make the best material for an
electromagnet?
A) wood
B) pencil lead
C) skin
D) iron
E) water