Electricity and Magnetism

Electricity and Magnetism

The basic units of electricity are voltage and current. Voltage is the unit of electrical force. Current is the unit of electrical flow. If a voltage is placed across a conductor such as a wire then electrical current will flow through the wire.

Fig. 1 Current flows when a voltage is placed across a conductor

By convention, current flows from + to -.

Alternating current (AC) is the type of electricity supplied through power lines. This voltage changes sinusoidally fifty times per second (known as 50 hertz). Direct current (DC) is the type of electricity which is supplied from a battery. This voltage stays at a constant level.

Fig. 2 Symbol for AC Supply Supply for DC Supply

Electricity and magnetism are related. Every electrical current causes a magnetic field.

Fig. 3 An electrical current flowing in a wire causes a magnetic field

The size and direction of the magnetic field depends on the size and direction of the electrical current. A large current causes a large magnetic field.