Transcript Magnets And Magnetic Fields

Crane Video
Electricity and magnetism are related!
Modeling  independent work  compare notes
Turn and talk
…Partner closer to the door
What is a magnetic field?
…Partner farther from the door
What causes a magnetic field?
Turn and talk
…Partner closer to the door
What is a magnetic field?
A magnetic field is an area around a
moving charge that exerts a force on
other moving charges / other
magnetized objects.
…Partner farther from the door
What causes a magnetic field?
Magnetic fields are creating by
moving charges / current.
Turn and talk
Compare and contrast electric fields and
magnetic fields.
Turn and talk
Compare and contrast electric fields and
magnetic fields.
Electric fields are areas around stationary
charges that can exert a force on other
charges. Magnetic fields are areas around
moving charges that can exert a force on
other moving charges / magnetized
objects.
Magnetic fields are created by moving electric charges
… where are the charges??
Magnetic fields are created by moving electric charges
… where are the charges??
Electromagnets
◦ Magnetic field created by electric current
◦ Can be turned on/off
◦ Examples: junk yard cranes, components of motors,
transformers, generators, speakers, etc.
Permanent Magnets
The charges are the spinning electrons of the atoms!
◦ All objects have spinning electrons, and each spinning
electron has a mini-magnetic field around it
◦ Usually, each mini-magnetic field points in a random
direction
◦ In a permanent magnet the mini-magnetic fields are
aligned
non-magnet
magnet
Permanent Magnets
The charges are the spinning electrons of the atoms!
Examples:
◦ Fridge magnets
◦ A compass needle
◦ The Earth!
Turn & Talk
Partner with longer last name…
◦ Compare and contrast permanent magnets and electromagnets
Partner with shorter last name …
◦ Identify an example of a permanent magnet and an
electromagnet
Magnets are Cool!
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North (+) Pole and South (-) Pole
 Opposite Attract
 Likes Repel
N
S
S
N
N
N
S
S
We can NEVER pull apart magnetic dipole. When we cut
magnet in two we end up with two smaller dipoles. If we keep
on cutting, more magnets will be produced, EACH with north
and south pole.
Let’s Break A Magnet!
Magnetic monopoles have never
been detected.
S
S
SNSN
N
N S
N
SNSN
We can NEVER pull apart magnetic dipole. When we cut
magnet in two we end up with two smaller dipoles. If we keep
on cutting, more magnets will be produced, EACH with north
and south pole.
Let’s Break A Magnet!
Magnetic monopoles have never
been detected.
S
S
SNSN
Just for fun …
Ever wonder why fridge
magnets don’t seem to have
poles … they do!
N
N S
N
SNSN
Earth’s A Magnet!
The poles received their names because of the behavior of a magnet in
the presence of the Earth’s magnetic field. The pole of a magnetic
needle that points to the north of the Earth is called north pole. So,
magnetic pole which is in the geographic north is magnetically south
pole.
Don’t freak out:
Earth's magnetic field has flipped
many times over the last billion years.
The Magnetic Field 𝑩
A magnetic field is said to exist at a point if a compass
needle placed there experiences a force.
The direction of the magnetic field at any location is the direction
in which the north pole of the compass needle points at that
location.
Field Lines of Bar Magnet
Magnetic field lines don’t start or stop.
There are no magnetic charges
(monopoles)
But don’t be confused if you see
pictures on the right
(technically wrong, but
commonly drawn)
– Arrows give direction to
which a north pole will
orient
– Density gives strength
– Looks like dipole!
-
+
Which diagram shows the
correct field lines of a
bar magnet?
(1)
(2)
(3)
Field lines
should always
point south
Field lines do
NOT stop
abruptly
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Place a magnet on a sheet of notebook paper
and trace its outline.
Move a compass around the magnet, and
sketch the field lines (where the north needle
points)
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Include definition, picture, and where appropriate, variable and
units and releavant equations.
electric field
magnetic field
charge
current
permanent magnet
electromagnet
resistance
potential
potential energy
power
work
force
Watch me!