Magnetism

A.  Characteristics of Magnets

1.  Magnetism is a property of matter where there is a force of attraction or repulsion between like or unlike poles.

2.  Magnetic forces are strongest near the ends of the poles.

3.  All magnets have a north (N) pole and a south (S) pole.

4.  Opposite poles attract; like poles repel.

5.  Magnetic fields are the areas around magnets where magnetic forces act.

6.  The magnetic domain theory states that groups of atoms in a material produce a magnetic field when they allign in the same direction.

B.  Uses of Magnetic Fields

1.  Electromagnets

a.  Electric current produces a magnetic field.

b.  Electromagnets are coils of wire that have magnetic fields when current is passed through them.

c.  Iron cores can make electromagnets stronger.

d.  Common uses of electromagnets:

1)  Doorbells

2)  Loudspeakers

3)  Construction and junkyard work

2.  Meters

a.  Ammeters are a form of galvanometer that measure electrical current when connected in series with the circuit.

b.  Voltmeters are another form that measure voltage when connected in parallel across a circuit.

3.  Motors

a.  Devices that change electrical energy into mechanical energy.

b.  As current is reversed in an electromagnet, a coil turns.

C.  Producing Electric Current

1.  Generators

a.  Devices that change mechanical energy into electrical energy.

b.  Moving a wire loop through a magnetic field produces a current in the wire.

c.  Generators produce most of our electricity.

d.  They are powered by water, wind or steam.

2.  Types of Electric Current

a.  Direct current

1)  DC

2)  Batteries

3)  Electrons flow only one direction.

b.  Alternating current

1)  AC

2)  Wall outlets

3)  Electrons are constantly moving back and forth.

3.  Transformers

a.  Current flows from from power plants at high voltages and must be reduced for our homes.

b.  Transformers either step up or step down the voltage.

1)  Step up transformers have more secondary coils than primary coils.

2)  Step down transformers have more primary than secondary coils.

c.  Voltage for wall outlets is 120V (dryers and stoves use 220V).

d.  Small devices step down the voltage even further.