Download Magnetism Study Guide

Magnetism Study Guide
** You need to also study the note packet for this unit. Using the study guide
alone is not enough. **
 A magnet is anything that attracts iron, nickel & cobalt. Steel contains iron, so it
is also magnetic material. Things that a magnet can attract include paper clips,
refrigerator doors and other magnets. Magnets only attract certain metals; so it
does not attract pennies, copper wire or aluminum.
 The parts of a magnet where the magnetic force is the greatest are called the
magnet’s poles.
 All magnets have a north pole and a south pole. There are no magnets that have
only one pole. If you cut a magnet in half you will end up with two smaller
magnets, each with a north and a south pole.
 The law of magnetic attraction says that opposite poles attract, and like poles
repel.
 Magnetic fields – are the places where a magnet’s effects can be felt – exist
around all magnets. You can show where a magnet’s field is by using magnetic
filings: small bits of magnetic material that are attracted to the magnet’s force.
Be sure you can look at the magnetic field of a magnet and decide where the
strongest and weakest part of the magnet lines are.
 You can tell where the poles of a magnet are, when looking at the field lines, by
looking for the place where the filings are most concentrated – bunched up
together.
 Groups of atoms that determine whether something is a magnet are called
domains.
 Objects are magnetized if the domains in the object are in alignment (which
means in straight lines, all pointing in the same direction).
 Magnets can be classified as either permanent magnets or temporary magnets.
 Temporary magnets (like the one described above) become magnetized easily,
but lose their magnetism easily. The domains of a temporary magnet are not
naturally aligned, but are forced into alignment by using a magnet or electricity.
This is why they lose their magnetism easily.
 A temporary magnet can lose its magnetism by making the domains go back out
of alignment. This often happens when a temporary magnet is dropped or hits a
hard surface. Sometimes it just happens over time, as the domains return to
their original state.
 Permanent magnets, on the other hand, have domains that are naturally aligned,
so they keep their magnetism. It is very hard to demagnetize a permanent
magnet, because their domains naturally align.
 Magnetism and electricity are connected. This connection is what allows us to
have a lot of the technology we have today, including all of our electrical
appliances, and heavy machinery at construction sites.
 You can use electricity to create magnets. Such magnets are called
electromagnets. The largest electromagnets are the ones that are used to carry
big, heavy beams on construction sites.
 An electromagnet is made of a solenoid, wrapped around an iron core, and
attached to an energy source.
 A solenoid is a coil of wire that produces a magnetic field when it carries an
electric current.
 You can make an electromagnet stronger by either (1) looping more coils in the
solenoid or (2) increasing the current running from the power source.
 Electromagnets can be turned off by stopping the electric current. This is a very
useful quality. Make sure you can explain an example where it could be useful.
 You can also use magnetism to create electricity. This happens moving a
magnet back and forth through a coil of wire that can carry electrical energy, like
copper wire. This is called electromagnetic induction.
 Electromagnetic induction is used by electric power plants every day, and
enables us to have energy to run our electrical appliances. They use generators
to convert mechanical (kinetic) energy into electric energy, by using
electromagnetic induction.
 Generators GENERATE electricity.
 Electric motors turn electric energy to mechanical/kinetic energy. In other words
they USE the electric energy (either from batteries, or from the sockets in the
walls) to make things work.