Chapter 21 Magnetism Section 1 What is Magnetism? Pages

Early Uses of Magnetism magnetite Thousands of years ago, people noticed that a mineral called magnetite attracted other pieces of magnetite and bits of iron. north When pieces of iron were free to turn, one end pointed north. compasses These might have been the first compasses. navigationexploration The compass was an important development for navigation and exploration.

Magnets Magnets attract objects made of iron or steel, such as nails and paper clips. Magnets can also attract or repel other magnets. polesnorth south Every magnet has two ends or poles….a north pole and a south pole. Like opposite Like poles repel each other and opposite poles attract each other.

The Magnetic Field pushpull move Remember a force is a push or pull that causes an object to move. magnetic force gravity A magnetic force can be exerted even when objects are not touching (just like gravity). weaker farther apart The magnetic force becomes weaker as the magnets get farther apart. magnetic field The magnetic force is exerted through a magnetic field.

Field Lines north south Magnetic field lines begin at a magnet’s north pole and end on the south pole. strong weaker The field lines are close together where the field is strong and get farther apart as the field gets weaker. According to the diagram, where is the magnetic field the strongest?. poles Near the poles.

Attraction and Repulsion attraction Field lines that curve toward each other show attraction. repulsion Field lines that curve away from each other show repulsion.

Making Magnetic Fields moving electron A moving electric charge, such as a moving electron, creates a magnetic field. magnetic domain A group of atoms, with their fields pointing in the same direction, is called a magnetic domain.

Magnetic Domains Microscopic sections Microscopic sections of iron and steel act as tiny magnets. randomly cancel each other. Normally, these domains are oriented randomly and their magnetic fields cancel each other. line up add When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

Earth’s Magnetic Field Earth Earth has a magnetic field similar to the field of a bar magnet. magnetosphere The region of space affected by Earth’s magnetic field is called the magnetosphere. One theory is the shifting One theory is the shifting molten iron of molten iron in the outer core of the Earth caused Earth’s magnetic field.

Nature’s Magnets natural magnets Some animals use natural magnets to detect Earth’s magnetic field to help them navigate. honeybees, rainbow trout, and homing pigeons Instead of using compasses, honeybees, rainbow trout, and homing pigeons have little pieces of magnetite in their bodies.

Earth’s Changing Magnetic Field stay in one place Earth’s magnetic poles do not stay in one place. 20 years ago The magnetic pole in the north is in a different location than where it was 20 years ago. reverses direction Sometimes Earth’s entire magnetic field reverses direction! (North Pole become South) This has happened more that 70 times This has happened more that 70 times in the past 20 million years.

The Compass compass needle A compass needle is a small bar magnet with a north and south magnetic pole. The north pole of the compass needle points toward Earth’s north magnetic pole The north pole of the compass needle points toward Earth’s north magnetic pole.