2.7 - AC & DC Current

Alternating and direct current

There are two types of electric current: alternating current (a.c.) and direct current (d.c.).

Direct current

• In direct current, the charges move in one direction only, so the current always flows the same way around the circuit.
• It's produced by a direct potential difference - a p.d. that stays positive, or stays negative, rather than switching between the two.
• Cells and batteries supply direct current.

Alternating current

• In alternating current, the current is constantly changing direction, flowing back and forth around the circuit.
• It's produced by an alternating potential difference, in which the positive and negative ends keep swapping over.
• The mains electricity supplied to homes is an alternating current.

UK mains supply

• The UK mains supply is an alternating current supply at about 230 V.
• Its frequency is 50 Hz (50 cycles per second).