Transcript Magnetism

Magnetism
Magnetic materials
All magnets have a North pole and a
South pole.
 Just like electric charges, like poles repel
and opposite poles attract.

Remember playing with magnets
as a kid?
Even breaking a magnet into smaller
pieces doesn’t remove the two poles.
Magnets produce magnetic fields
How to draw magnetic field lines
Magnetic field lines
are always drawn
outward from the
North pole and
inward to the
South pole.
 The magnetic field
is strongest where
the field lines are
closest together.

Similar to electric field lines!
So how do paper clips stick to a
magnet?
The Earth even has a magnetic
field!

In response to the
Earth's magnetic
field, the compass
will point toward
the geographic
North Pole of the
Earth because it is
in fact a magnetic
south pole. The
magnetic field lines
of the Earth enter
the Earth near the
geographic North
Pole.
Applications of Magnetism
 Compasses
 CD
and DVD files
 Audio and video cassette recording
 MRI scans
 Aurora borealis
 Homing pigeons (what?!)
 Electric generators
 Transformers
Some of those applications are
related to electricity – why are they
here?
 Hans
Christian Oersted discovered
that an electric current produces a
magnetic field.
– 1st right hand rule
 Michael
Faraday proved the reverse
to be true; that a magnetic field
produces an electric current
(induction)
EMF
 Electromagnetic
induction is the
generation of an electromotive force
(EMF) in a conductor when it’s
exposed to a magnetic field.
 Measured in volts (J/C) so it’s the
same as potential difference!
 Faraday’s Law
 Useful in generators and
transformers
1st right hand rule
magnetic field around a current-carrying wire
1st right hand rule
magnetic field around a current-carrying wire
2nd right hand rule
direction of field around a solenoid (wire coil)
2nd right hand rule
direction of field around an electromagnet or
solenoid
Relationships
 The
higher the current (I), the
stronger the magnetic field.
 The higher the number of turns (N)
in the electromagnet, the stronger
the magnetic field.
 The voltage is proportional to the
number of loops