Magnets
A magnet is an object or material that attracts certain metals, such as iron, nickel and cobalt. It can also attract or repel another magnet. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and like poles repel each other. Various electrical devices make use of magnets.
Questions you may have include:
- What types of magnets are there?
- What are some common properties of magnets?
Types of magnets
There are permanent magnets, temporary magnets and electromagnets.
Permanent magnets
A permanent magnet is one that will hold its magnetic properties over a long period of time.
Magnetite
Magnetite is a magnetic material found in nature. It is a permanent magnet, but it is relatively weak.
Alloys
Most permanent magnets we use are manufactured and are a combination or alloy of iron, nickel and cobalt. Rare-earth permanent magnets are a special type of magnet that can have extreme strength.
Temporary magnets
A temporary magnet is one that will lose its magnetism. For example, soft iron can be made into a temporary magnet, but it will lose its magnetic power in a short while.
Electromagnet
By wrapping a wire around an iron or steel core and running an electrical current through the wire, you can magnetize the metal and make an electromagnet. If the core is soft iron, the magnetism will diminish as soon as the current is turned off. This feature makes electromagnets good for picking up and dropping objects. Typically DC electricity is used, but AC current will also result in an electromagnet.
Properties of magnets
Magnets always have two poles, come in various shapes, and attract or repel other magnets.
Names of poles
All magnets have a North-seeking pole (N) and South-seeking pole (S). In a compass, the side marked (N) will point toward the Earth's North magnetic pole. Thus, it is called the "North-seeking pole." Also note that the Earth's North magnetic pole is not the same thing as the North Pole. They are actually several hundred miles apart.
NOTE: To avoid confusion, you should try to be exact in what you are describing, especially concerning magnets.
Various shapes
The magnet can be made into various shapes. The bar magnet is the most common configuration.
Magnets also can be square, spherical, shaped like a horseshoe, and even shaped like a donut.
If you put an iron plate across the N and S poles of a horseshoe magnet, that would essentially "short circuit" the effect of the magnetism, such that its strength would not be very great. As soon as the plate was removed, the magnet would regain its full strength. That method is sometimes used in magnets that are temporary to help keep their magnetic properties for a longer time.
Cutting a magnet
An interesting characteristic of magnets is that when you cut a magnet into parts, each part will have both N and S poles.
Attraction and repulsion
Magnets strongly attract iron, nickel and cobalt, as well as combinations or alloys of these metals.
Also, unlike poles of two magnets will attract, but like poles will repel. Thus, N and S attract, while S and S will repel each other.
Applications
There are numerous applications of magnets.
Creating a magnet
You can magnetize a piece of steel by rubbing a magnet in one direction along the steel. This lines up the many of the domains or sections of aligned atoms in the steel, such that it acts like a magnet. The steel often won't remain magnetized for a very long time, while the true magnet is "permanently" magnetized and retains its strength for a long time.
If you use soft iron or steel, such as a paper clip, it will lose its magnetism quickly. Also, you can disorient the atoms in a magnetized needle by heating it or by dropping the needle on a hard object.
Compass
The first true application of a magnet was the compass, which not only helps in navigation by pointing toward the North magnetic pole, but it is also useful in detecting small magnetic fields. A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.
Other uses
Magnets are found in loudspeakers, electrical motors and electrical generators.
A very common application of magnets is to stick things to the refrigerator. Since the outer shell of most refrigerators is made of steel, a magnet will readily stick to it. The type of magnets used often consists of a thin sheet of a magnetic material.
As a novelty, magnetic disks can be stacked on a pencil to show magnetic levitation.
Summary
A magnet attracts iron, nickel, cobalt and combinations of those metals. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and similar poles repel each other. Magnets are found in many of our electrical appliances.