Chapter 16 Section 1 Objective: Describe the properties of magnets. Explain why some materials are magnetic and some are not. Describe four kinds of magnets. Give two examples of the effect of Earth’s magnetic field.

Properties: Magnetic Poles are points on a magnet that have opposite magnetic qualities. The pole of a magnet that points to the north is called the magnet’s north pole. The opposite end of the magnet, called the south pole, points to the south.

When you bring two magnets close together, the magnets each exert a magnetic force on the other. These magnetic forces result from spinning electric charges in the magnets. The force can either push the magnets apart of pull them together.

A magnetic field exists in the region around a magnet in which magnetic forces can act.

Why are some materials magnetic and some not?

In materials such as iron, nickel, and cobalt, groups of atoms are in tiny areas called domains. The north and south poles of the atoms in a domain line up and make a strong magnetic field.

Losing Alignment - When domains move, the magnet is demagnetized, or loses its magnetic properties. Making Magnets - You can make a magnet from demagnetized material if you line up its domains with another magnet. When you cut a magnet in half, you end up with two magnets.

Some magnets, called ferromagnets, are made of iron, nickel, cobalt, or mixtures of those metals. Another kind of magnet is the electromagnet. This is a magnet made by an electric current. Temporary magnets are made from materials that are easy to magnetize. But they tend to lose their magnetization easily. Permanent magnets are difficult to magnetize, but tend to keep their magnetic properties longer.

Name two examples of the effect of Earth’s magnetic field.

The Earth behaves as if it has a bar magnet running through its center. The point of a compass needle is attracted to the south pole of a magnet. Opposite poles of magnets attract each other. A compass needle points north because the magnetic pole of Earth that is closest to the geographic North Pole is a magnetic south pole.

Scientists think that the Earth’s magnetic field is made by the movement of electric charges in the Earth’s core. Earth’s magnetic field plays a part in making auroras. An aurora is formed when charged particles from the sun hit oxygen and nitrogen atoms in the air.

Chapter 16 Section 2 Objective: Identify the relationship between an electric current and a magnetic field. Compare solenoids and electromagnets.

electromagnetism—the interaction between electricity and magnetism.

A solenoid is a coil of wire that produces a magnetic field when carrying an electric current. An electromagnet is made up of a solenoid wrapped around an iron core. Electromagnets are very useful because they can be turned on and off as needed. The solenoid has a field only when there is electric current in it.

Chapter 16 Section 3 Objective: Explain how a magnetic field can make an electric current. Explain how electromagnetic induction is used in a generator. Compare step-up and step-down transformers.

Michael Faraday conducted an experiment trying to get the magnetic field of the electromagnet to make an electric current in a second wire.

Faraday realized that electric current in the second wire was made only when the magnetic field was changing. The process by which an electric current is made by changing a magnetic field is called electromagnetic induction.

The electric current produced by the generator changes direction each time the coil makes a half turn. Because the electric current changes direction, it is an alternating current. The energy that generators convert into electrical energy comes from different sources such as fossil fuels and nuclear energy.

A transformer increases or decreases the voltage of alternating current. The number of loops in the primary and secondary coils of a transformer determines whether it increases or decreases the voltage. The electric current that brings electrical energy to your home is usually transformed three times.