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Magnets
Two poles of the same kind repel each other.
Two poles of the opposite kind attract each other.
1
Field lines
The lines show the
direction of force
on a north pole.
In the early 1800’s,
Michael Faraday notes
that iron filings line up
around a magnet to
show “force field lines”.
2
Electromagnets
In 1820 Hans Christien Ørsted
discovers that an electric current
in a wire creates a magnetic
field. This is the principle behind
the electromagnet.
3
Lorentz force
In 1892 Hendrick Lorentz discovers that a
current-carrying wire feels a force when it
is in a magnetic field. This is the principle
behind the electric motor.
The force on the electrons
is out of the page.
Why did it take him so long???
The force on the current is
perpendicular to the magnetic field
and perpendicular to the current.
(If the current is in the same direction
as the field, there is no force.)
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