Electromagnetism

Kevin BrackenSmyrna Middle

6-32007

Magnets and Magnetism

• Can stick to each other.

• Can stick to some types of metals.

• Can stick to other objects without actually touching the object.

Properties of magnets

• Discovered more than 2,000 years ago.

• Found in Magnesia, so the Greeks called it Magnetite.

• Today any material that attracts iron or materials containing iron is called a magnet.

• All have two poles, exert forces and are surrounded by a magnetic field.

Magnetic Poles

• The parts of the magnet where the magnetic field is strongest.

• On a bar magnet, the poles are on each end.

• Always occurs in pairs.• The pole that points north is called the

north pole.• The pole that points south is called the

south pole.

Magnetic Forces

• The force of repulsion or attraction between the poles of a magnet is called the magnetic force.

• Like poles repel. (Push away)

• Opposite poles attract. (Come together)

Magnetic Fields

• The field lines can be drawn from the north pole to the south pole of a magnetic.

• The closer the field lines the stronger the field.

What Makes Materials Magnetic

• It depends on the atoms.

• If the atoms in a domain are all lined up the material is magnetic.

• Iron, nickel, and cobalt are all magnetic.

Losing Alignment

• Dropping

• Hitting it too hard

• Heating

Making Magnets

• Aligning domains can cause an object to become magnetized.

• You can do this by taking a magnet and rubbing it in one direction over and over again on an object.

Domains

The photo on the left shows what happens to the field lines when domains are not aligned, the photo on the right shows a magnet with its domains aligned.

Half a Magnet?

If you cut a magnet in half you end up with two smaller magnets, each with a north and south pole.

This is because of those tiny domains inside every magnet.

Types of Magnets

• Ferromagnets– Nickel, Cobalt, and Iron

Magnetite is a naturally occurring Ferromagnet.

Electromagnets- have an iron core and has an electric current.

Temporary and Permanent

• Temporary easy magnetize, and easy to lose magnetism.

• Permanent- difficult to magnetize and difficult to lose magnetism.– Alnico-made from

• Nickel, Cobalt, Aluminum

Earth as Magnet

• Earth’s solid inner core is surrounded by a fluid outer core.

• This flow of metals creates an electric field and acts like a bar magnet.

• This helps to create the northern lights.

Magnetism from Electricity

• Maglev trains have been created that use magnets and electricity to move.

The Discovery of Electromagnetism

• Hans Christian Oersted (1820).

• Held a compass near a wire carrying an electric current.– This threw off the orientation of the compass

needle.– When he reversed the current the magnetic

field reversed.

Take a break

• …..to be continued tomorrow…..

Using Electromagnetism

• You can increase the strength of the magnetic field by adding a current carrying wire.

• Solenoids– Coil of wire that produces a magnetic field when

carrying an electric current.

• Electromagnets– Magnet consisting of a solenoid wrapped around an

iron core.

• Heavy Lifting– Electromagnets can be turned off and on.

Ways to Increase the Strength of an Electromagnet

• Increase the number of loops in the solenoid.

• Add or increase the size of the iron core.

• Increasing the current in the wire.

Uses (Applications) of Electromagnetism

• Doorbells

• Electric Motors

• Galvanometers

• Lifting Heavy Objects

Electricity From Magnetism

• Faraday wrapped a current carrying wire around half of an iron ring and wrapped the other side with a wire connected to a galvanometer.

• The only activity he recorded was at hook-up and disconnection.

• Electric current was produced in the second wire only when the magnetic field was changing.

Some of Faraday’s Set-Ups

What Faraday Learned

• Adding more coils increased the electric current.

• Moving the magnet faster produces a greater electric current as well.

Applications of Electromagnetic Induction

• Generators– Often used as back-up power.– The coil of wire is turned.– Produces alternating or AC current.

• Generating Electrical Energy– Huge magnets are turned to create the power.– Used by nuclear, hydroelectric, and fossil fuel plants.

• Transformers– Used to step-up (increase) or step-down (decrease)

voltage.

How Electricity Gets to Your Home