Transcript Magnetism (High School)

Magnetism
Properties of Magnets
 All magnets have two areas of strongest force, called
poles.
 Each magnet has one north pole and one south pole.
 Like poles repel, and opposite poles attract.
 The magnetic region where you can “feel the force” is
called a magnetic field.
Magnetic Materials
 What makes some things

magnetic, while other things
can’t be magnetized?
 Spinning electrons cause small
magnetic fields around each
atom.
 Magnetic materials have atoms
whose magnetic fields can be 
lined up in the same direction.
 Areas where atoms’ magnetic
fields line up are called
magnetic domains.
magnetic domain
Randomly arranged domains =
No magnet!
Magnetic domains lined up =
Magnet!
The Earth is a magnet!
magnetic north pole
geographic north pole
magnetic south pole
geographic south pole
 Magnetic lines of force around
the earth are like the field
lines around a giant bar
magnet.
 The magnetic north pole and
the geographic north pole are
not located in the same place!
 The north pole of a compass
points to the earth’s magnetic
north pole.
Electricity to Magnetism
 In 1820, H.C. Oersted
discovered that an electric
current flowing through a wire
had a magnetic field around it.
 Electricity can cause
magnetism!
 Electromagnets are powerful
magnets that can be turned on
and off.
 You can make an
electromagnet stronger by (1)
putting more turns of wire in
the coil or (2) making a larger
soft iron core, or (3)
increasing the current through
the wire.
Uses for electromagnets
 A simple DC electric motor
contains a permanent magnet, an
electromagnet, and a commutator.
When current flows through the
electromagnet, it turns within the
magnetic field of the permanent
magnet, changing electricity to
mechanical energy.
 Current meters also use permanent
magnets and electromagnets.
When current flows through a wire,
it makes an electromagnet. The
force between the electromagnet
and the permanent magnet makes
a needle move on the meter.
Magnetism to Electricity
 Joseph Henry and Michael
Faraday discovered that
magnetism could also produce
electric current. This is called
 If a magnet is moved back and
forth through a coil of wire,
current can be made to flow
through the wire. This is the
idea behind electric generators
and transformers.
Current moves left in wire.
Current moves right in wire.
electromagnetic induction.
Uses for Electromagnetic
Induction
 Generators produce AC current
for home and industrial use.
Water, wind, or steam are
used to move large
electromagnets through the
coils of wire to produce
current.
 Transformers are used to step
up voltage of electricity that
must travel long distances
through wires. Other
transformers then step down
the voltage before it enters
our homes.