Magnetism and
electromagnetic induction
Magnets and magnetic fields
Behavior of electric charge in a
magnetic field
Magnets are bipolar
„
„
Every magnet has a
north pole and a
south pole
Like poles repel
each other; opposite
poles attract
1
Magnets are bipolar
„
„
„
Every magnet has a
north pole and a
south pole
Like poles repel
each other; opposite
poles attract
Breaking a magnet
gives you two
magnets
Magnetic field lines run from
north pole to south pole
„
This can be followed
with iron dust and a
piece of paper
„
demonstration
2
Compasses align with the
Earth’s field lines
„
Which way are the
forces operating?
„
„
„
What is the net
force?
Why does the needle
turn?
Demonstration of
Earth’s magnetic
field
Magnetic domains
„
„
Every magnetic material
has “magnetic domains”
Random orientation
until brought into
external magnetic field
„
„
Domains can then be
aligned
Shocks will knock them
out of alignment
3
Electric currents produce
magnetic fields
„
„
The field is
perpendicular to the
axis of current flow
Field lines surround
the wire
„
Different wire
configurations give
different field
configurations
Magnetic fields exert force on charge
particles, including electric currents
„
„
„
Current-carrying wires are deflected by magnets
Deflection depends on current direction
Current-carrying wires generate their own fields
„
Therefore attract or repel each other
4
Cosmic rays in the Earth’s
magnetic field
Putting this to work:
DC electric motors
5