Magnetism

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Magnetic lines of force of a bar magnet shown by iron filings on paper
Representation of the electric field vector of a wave of electromagnetic radiation circularly polarized.

In physics, magnetism is a force that can attract (pull closer) or repel (push away) things (objects) that have a magnetic material like iron inside them (magnetic objects).

Magnets[change | change source]

Magnetism can be made by things we call magnets, or can also be made by electricity in a wire (called an electromagnet). Magnetic attraction is when magnets are put near to magnetic objects, the magnet will attract the magnetic object and pull it towards the magnet until it is as near as it can get or touching it. Magnets can also repel other magnets. Most objects that are attracted to magnets have iron in them. Most other metals, such as aluminium, are not attracted to magnets.

Magnetic Fields[change | change source]

Magnets have an unseen area around them called a "magnetic field." Magnetic objects inside this unseen field are attracted to the magnet. Magnetic things outside the magnetic field are not attracted to the magnet. This is why a magnet must be close to an object to attract it.

Magnetic Poles[change | change source]

The ends of a magnet are called magnetic poles. This is the part of magnets that attract magnetic things the most. All magnets have what is called a magnetic north pole and what is called a magnetic south pole. If a piece of string is tied to the middle of the magnet and the string is held so that the magnet is allowed to hang down on its own, then the north pole of the magnet will turn and point to the Earth's North Magnetic Pole. This can be tested by tying a string to a magnet shaped like a straight stick, and then holding the string so that the magnet can turn up and down and around.

The poles of two magnets will repel or attract each other. Different poles attract each other. For example, if the south pole of one magnet is put near the south pole of another magnet, the magnets will repel each other. This will also happen with two north poles that are put near each other. If a north pole is put near a south pole, the magnets will attract each other until they stick to each other and can be hard to pull apart.

Magnetic Domains[change | change source]

Magnetism is caused by electrons (the negative particles in atoms that are also electric charges) spinning. The more a group of electrons spin in the same direction, the stronger the magnetic force. In a magnet, many electrons are spinning in the same direction.

We can magnetize a small piece of iron by 'rubbing' it with a magnet. The electrons in the iron get 'spun' by the passing magnet just like a basketball player spinning a basketball.

Uses of Magnets[change | change source]

Magnets have many uses. One of them was found long ago when explorers found that a magnet could be used as a compass to show the direction of north & south.

Electromagnets and Electromagnetism[change | change source]

Electromagnets are another kind of magnet. They only work when electricity is running through them. An electric current makes a magnetic field. If you wrap the wire into a coil, the electrons spin around the coil and make a stronger magnetic domain.

Often, these magnets work by using a coil of wire that makes a magnetic field when there is a current in it. In addition to this coil of wire, a large piece of metal, usually iron, is placed inside the coil to increase the magnetic field made. Though most large electromagnets employ many solenoids to lift heavy objects, smaller solenoids are used in everyday electronics. For example, they are used to change voltage in a transformer. Electromagnets can also be used to make electricity. Movement of a magnet back and forth in front of the electromagnet will make an electric current.

Uses of Electromagnets[change | change source]

Electromagnets are used to make many things work like computers, televisions and radios and also doorbells.

Effects[change | change source]

The effect of magnetism on global warming has not yet been studied. It is believed that severe climate change can also change the Earth's magnetism. This has not been found to be true yet. Earth does change its magnetic poles every million years (plus or minus 200,000 years). Before a change of magnetic field, the Earth's magnetic field becomes weaker and moves around, like a top would before it falls. The earth has already had hundreds of changes (flip flops). Scientists know this as a result of studies of the sea floor, near the mid-Atlantic ridge. The lava slowly moves out of this crevasse (gap in the sea floor) and then it cools with its iron molecules all pointing in the new direction of the Earth's magnetic field. We can look at the history of this magnetic field today to look back at the many flips in the past.

Electromagnetic waves[change | change source]

Electromagnetic radiation including radio waves and light waves are used for communication including broadcasting and optical fiber, and for many other purposes.

Other websites[change | change source]