Magnetism

Magnets have been known for centuries 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? Magnetism is the attraction of a magnet for another object

Magnets A magnet will pull some metals towards itself. Metals that contain iron, nickel, and cobalt are magnetic. In other words, a magnet will pull them. Magnets are made of iron, nickel, or cobalt

The ends of a magnet are where the magnetic effect is the strongest The ends of a magnet are where the magnetic effect is the strongest. These are called “poles.” Each magnet has 2 poles – 1 north, 1 south.

For Every North, There is a South Every magnet has at least one north pole and one south pole.  By convention, we say that the magnetic field lines leave the North end of a magnet and enter the South end of a magnet.  If you take a bar magnet and break it into two pieces, each piece will again have a North pole and a South pole.  If you take one of those pieces and break it into two, each of the smaller pieces will have a North pole and a South pole.  No matter how small the pieces of the magnet become, each piece will have a North pole and a South pole.  S N S N S N

Breaking Magnets

How to break a magnet: Heat it Drop it Strike it hard This causes the domains to become random again!

Every magnet has a north pole and a south pole.

Like repels like Opposites attract

The region where the magnetic forces Magnetic Fields The region where the magnetic forces act is called the “magnetic field”

Magnetic Field Every magnet has a magnetic field around it. It can be thought of as a line of force running from the north end of the magnet to the south end of a magnet. Earth’s magnetic field is what causes the needle of a compass to point north and south.

Magnetic Domain Atoms themselves have magnetic properties due to the spin of the atom’s electrons. Groups of atoms join so that their magnetic fields are all going in the same direction These areas of atoms are called “domains” The entire domain acts like a magnet with a north and a south pole

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

An unmagnetized substance looks like this…

While a magnetized substance Looks like this…

Magnetic Domains Magnetic force lines.

What do you know of that has a North and South Pole? The Earth is one giant magnet. It has two magnetic poles and is surrounded by a magnetic field. This magnetic field is what causes the needle of a compass to point in different directions and causes the poles of a magnet to point either north or south.

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.

Like many Planets in our Solar System the Earth has a Magnetic Field

The Earth acts like a magnet It exerts magnetic forces and is surrounded by a magnetic field that is strongest near the North and South magnetic poles Magnetic South Pole Geographic North Pole Magnetic North Pole Geographic South Pole

The Earth behaves as if there was a magnet in its interior.

The North Pole of the Earth has a “south” polarity

As a result a compass will always point towards the North

A compass is a Magnetized piece of metal that can spin.

A compass is a Magnetized piece of metal that can spin. North attracts South S The north tip of the compass always points towards the North Pole of the Earth N

A Magnetic Field also protects us from the Solar Wind

The Sun produces a stream of charged particles that spread throughout the solar system.

These particles are deflected by the Earth’s Magnetic Field

The Earth’s magnetic field extends far into space 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 Video Here

Magnetic Declination

Electromagnets An electromagnet can be used to move large quantities of metal. When the current is on the magnet will pick up the metal. When you want to drop it you turn off the power and the electromagnet is disabled and the metal drops.

Electromagnet A temporary magnet made by passing electric current through a wire coiled around an iron bar. A junkyard is one place to see an electromagnet in action. A crane holding a huge electromagnet can be used to pick up scrap metal when current flows through it. When the crane operator wants to drop the scrap, he or she will simply shut off the current to the electromagnet.

In an electromagnet the electrons move around an iron nail + -

Magnets and electricity Magnets are used to generate, or produce, electricity. Spinning a coil of wire inside a magnetic field produces an electric force between the ends of the coil. In a similar way, an electric current produces a magnetic field around it.

Electromagnets An electromagnet consists of an iron core placed inside a wire coil. The magnetic field strength of a wire coil carrying an electric current increases in direct proportion to the number of turns of the coil.

Electric Motors An electric motor uses the sideways push of a magnetic field to turn a current-carrying wire loop. Electric motors use a commutator to change the direction of the current in the loop. Alternating current electric motors do not use commutators.

Oersted’s Experiment Hans Christian Oersted discovered in 1820 that an electric current near a compass causes the compass needle to be deflected. Oersted's experiment showed that every electric current has a magnetic field surrounding it.

Uses of magnets Magnets were first put to use in navigation because they always point north and south. Magnets are used to hold, separate, control, convey and elevate products and to convert electrical energy into mechanical energy or convert mechanical energy into electrical energy.

Magnet Activity

We use magnets in many ways! Which of the following items in a home use a magnet? Blender washer dryer Radio can opener dishwasher Refrigerator doorbell compass Click here to find out! (select kitchen on the left of the screen, close window to return to this presentation) Magnet Activity

Magnets around the House: Headphones Refrigerator magnets Computer speakers Telephone receivers Phone ringers Microwave tubes Seal around refrigerator door Plug-in battery eliminators Floppy disk recording and reading head Audio tape recording and playback head Video tape recording and playback head Credit card magnetic strip TV deflection coil Computer monitor Computer hard drive Shower curtain weights / attach to tub Power supply transformers

Magnets inside of motors: CD and DVD spinner and head positioner Audio and VHS tape transport VHS tape loader Microwave stirring fans Kitchen exhaust fans Garbage disposal motor Sump pump Furnace blower and exhaust    Garage door opener Bathroom exhaust fan Electric toothbrush Ceiling fan Pager or cell phone vibrator Clocks (not the wind-up type or LCD type) Computers    

http://science.pppst.com/magnets.html