What is magnetism?

What is magnetism?Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.

What is Magnetism?

• Magnets have been known for centuries.

• The Chinese and Greeks knew about the “magical” properties of magnets. The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation.

What is Magnetism?

• Magnets produce magnetic forces and have magnetic field lines

Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together.

Unlike poles of magnets attract each other and like poles of magnets repel.

Magnetic Fields

The area around a magnet where magnetic forces act

Magnetic Lines of Force

• Imaginary lines that show the shape of the magnetic force.– Closest at the poles

where magnet is the strongest.

Like repels like…

Opposites attract!

Poles of a magnet always

Come in pairs!

If you cut a magnet in half,

you get 2 magnets!

S N S N S N

If you cut it again, you get more magnets . . .

What are magnetic domains?Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. These domains are typically composed of billions of atoms.

Atoms themselves have magnetic properties due to the spin of the atom’s electrons.

These areas of atoms are called “domains”

Groups of atoms join so that their magnetic fields are all going in the same direction

Magnetic Domains

When an unmagnetized substance is placed in a magneticfield, the substance can become magnetized.This happens when the spinning electrons line up in thesame direction.

Magnetic Domains

How to break a magnet:

1. Drop it

2. Heat itThis causes the domains to become random again!

Temporary Magnets

William Gilbert, an English physician, first proposed in 1600 that the earth itself is a magnet, and he predicted that the Earth would be found to have magnetic poles.

The Earth is a magnet:It exerts magnetic forces and is surrounded by amagnetic field that is strongest near theNorth and South magnetic poles

The earth is like a giant magnet!

The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

We use the Earth’s magnetic field to find direction.

The needle of a compass always points toward the magnetic south pole.

We call this direction “North” (remember, opposites attract)

The sun has a magnetic field, too. It extends far above the sun’s surface.

Other planets in the solar system also have these magnetic fields

When a charged particle enters a magnetic field, an electric force is exerted on it. If a charged particle moves at an angle to a magnetic field, the magnetic force acting on it will cause it to move in a spiral around the magnetic field lines.

The solar wind is constantly bombarding the Earth’s magnetic field. Sometimes these charged particles penetrate that field. These particles are found in two large regions known as the Van Allen Belts.

The Earth’s magnetic field extends far into space. It is called the “magnetosphere.”

When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

The Aurora Borealis in the Northern Hemisphere

And the Aurora Australis in the Southern Hemisphere

Electricity and Magnetism – how are they related?When an electric current passes through a wire a magnetic field is formed.

What is an electromagnet?When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

What is a galvanometer?A galvanometer is an electromagnet that interacts with a permanent magnet. The stronger the electric current passing through the electromagnet, the more is interacts with the permanent magnet.

The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

Galvanometers are used as gauges in cars and many other applications.

What are electric motors?An electric motor is a device which changes electrical energy into mechanical energy.

Go to the next slide

How does an electric motor work?

Simple as that!!

We have seen how electricity can produce a magnetic field, but a magnetic field can also produce electricity! How?

What is electromagnetic induction?

Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction.

A generator is used to convert mechanical energy into electrical energy by electromagnetic induction.

Carefully study the next diagrams:

Direct current versus alternating current – AC vs DC : What’s the difference?

Direct current is electrical current which comes from a battery which supplies a constant flow of electricity in one direction.

Alternating current is electrical current which comes from a generator. As the electromagnet is rotated in the permanent magnet the direction of the current alternates once for every revolution.

Go to this website and click the button for DC then for AC to visually see the difference between the two.

You can see that the DC source is a battery – current flows in one direction. The AC source is the generator and the current alternates once for each revolution.