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# Physical Science Study Guide for McGraw-Hill's ASVAB (page 5)

By McGraw-Hill Professional
Updated on Jun 26, 2011

### Magnetism

Magnets can be made by placing a certain material, such as iron or steel, in a strong magnetic field. Pieces of the steel or iron are generally arranged in a random order. When these pieces, or domains, are placed in a strong magnetic field, they line up in the direction of the field. When most of the domains are aligned, the material becomes a magnet.

A bar magnet has three-dimensional lines of force around it on all sides. If the lines were visible, they would look like the following diagram.

When opposite poles of two magnets are brought together, the lines of force join up and the magnets pull together.

When like poles of two magnets are brought together, the magnets repel each other and the lines of force push away.

Earth as a Magnet   Because of its iron-nickel core, Earth behaves like a giant magnet. It happens that Earth's magnetic poles are fairly close to the geographic poles. A compass has a needle that is attracted to the magnetic north pole and is repelled by the magnetic south pole.

Earth's magnetic field, called a magnetosphere, is produced by electric currents. Deep in Earth's core, there is convection as hot molten magma rises, cools, and sinks. The process repeats itself time and time again. Within these rising and falling masses of magma, the rotation of Earth creates organized patterns of circular electric currents, called eddies. The interior of Earth seems to act like a giant dynamo. Earth's magnetic field deflects most of the charged particles streaming from the sun.

Magnets are used to make electric motors and generators. Generators produce electricity, which supports our lifestyle in many ways.

Electricity and Magnetism   The movement of electrons around the nucleus of an atom produces a magnetic field. The wire that contains an electric current is surrounded by a magnetic field. A wire with a current running through it that is wrapped around an iron core is called an electromagnet. Electromagnets are used in a variety of ways in our lives in everything from doorbells to magnetic high-speed trains.