CHAPTER 8 MAGNETISM AND ITS USES

SECTION 1 MAGNETISM ► All magnets have a north pole and a south pole ► Like poles repel, and unlike poles attract ► Magnetic materials--iron, cobalt, and nickel ► Permanent magnets are made by placing a magnetic material in a strong magnetic field

SECTION 2 ELECTRICITY AND MAGNETISM ► Moving charges, like those in an electric current, produce magnetic fields  The strength of the magnetic field depends on the amount of current flowing through the wire ► Electromagnet—a temporary magnet made by placing a piece of iron inside a current-carrying coil of wire  Magnetic field is present only when current is flowing in the wire coil  Increase strength of the magnetic field by adding more coils to the wire coil or increasing the current passing through the wire ► Converts electrical energy into mechanical energy to do work

► Galvanometer—a device that uses an electromagnet to measure electric current ► Electric motor—a device that changes electrical energy into mechanical energy.

SECTION 3 PRODUCING ELECTRIC CURRENT ► Generator—a device that converts mechanical energy to electrical energy ► Direct current (DC) is current that flows in one direction through a wire ► Alternating current (AC) reverses the direction of the current flow in a regular way

► Transformer —a device that increases or decreases the voltage of an alternating current  A step-up transformer increases voltage  A step-down transformer decreases voltage  Power carried in power lines as high as 750,000 V is reduced by step down transformers to household current (AC) of 120 V