MAGNETISMMAGNETISM

The Earth

Magnetic Poles

North and South

Geographic Poles

North and South

Earth is a giant magnet.

Magnetic Declination

InclinometerAn example of an inclinometer showing the Earth’s magnetic inclination

Compass PointsThe direction of compass points in United States

Types of Magnets

LOADSTONE

BAR

UCOIL ALNICO

Natural Magnet

Material is Magnetite or Iron Oxide (Fe2 03)

Magnets

A very strong magnet can be made with a coil of wire and the flow of an electric current.

Alnico

An extremely strong Alnico permanent magnet with keeper

Theory of Magnetism

Molecular and Electron Theories

Creating Magnets

The picture shows that a screwdriver does not pick up paper clips.

Methods used to create a magnet

Creating MagnetsStroking using a permanent magnet

However, after stroking the screwdriver with a magnet, the blade itself becomes magnetic and attracts the paper clips.

Flux

Magnetic lines of force

Strongest at the poles

Removing Magnetism

Heat is one way to remove magnetism.

Laws of Magnets

Poles attract or repel

Like Poles Repel

Laws of magnets shown by flux lines

Unlike poles attract Like poles repel

Stray Lines of Force

Controlling stray lines using a keeper

Magnetic Lines of Force

Notice how the materials are affected

Soft iron is a material that distorts flux

Magnetism will pass through any material

Electromagnetism

Electromagnets

A 30-foot diameter electromagnet

used in research for a superconductor

A large electromagnetused to lift scrap metal

ElectromagnetsThe source of electromagnetism is electricity (current) flowing through a coil of wire.

Electromagnets

A coil of wire can be made into a magnet by passing an electric current through it.

Without electricity, there is no magnetic force

Electric current applied to a coil creates a magnetic field

Electromagnetic Strength

Increase the number of coils. Increase the electric current flowing through

the coil. Add an iron core in the center of the coil.

How can an electromagnet be made stronger?

Electromagnetic Strength

The left hand rule to determine North Pole

NORTH POLE SOUTH POLE

Making a Magnet

An example of a very strong magnet

The magnet is strong enough to lift this 50 pound engine cylinder head.

The coil of wire has been attached to a 12 volt DC power source making an extremely strong magnet.

Making a Magnet

Saturation

Saturation KneeY- Axis

Increasing

Magnetic

Force

Y

X- Axis Increasing Electric Current

X

Saturation of a magnetic field occurs when an increase of electric current flow does not increase the strength of the magnetic field as shown by the graph. The knee of the curve is the point that saturation occurs.

MAGNETIC COIL LOSSES

Copper losses - resistance of copper coils.

Hysteresis - magnetic flux inducing a current in the core.

Eddy currents - magnetic polarity of the iron core is rapidly changed by an AC current causing friction and heat between the molecules

ELECTROMAGNETIC DEVICES

Electromagnetic Devices

Electromagnetic Devices

MAGNETIC TERMS

Flux - Invisible lines of force. Poles - North and South where force is

strongest. Permeability – The ability of a material to

conduct lines of force. Residual Magnetism – The ability of a

material to hold its magnetism for a long time.

MAGNETIC TERMS

Ferromagnetic Material – A material easy to magnetize. (i.e., Iron Steel, Cobalt, Perm-alloy, and Alnico)

Paramagnetic Material- A material that can be slightly magnetized.

Diamagnetic Material – A material that is very difficult to magnetize.

Magnetic Laws – Simply stated: Like poles repel and unlike poles attract.

Review

What are the poles of a magnet? Name the magnetic lines of force. List five types of magnets and their two

families. List the laws of magnets. Explain two methods for making a magnet.

Review

Explain two theories of magnetism. Name five different types of devices that are

associated with electromagnetism? List three magnetic and three nonmagnetic

materials. What will remove magnetic lines of force?