**1.10 Electricity Fundamentals**

**Direct Current**

Personal Computer systems are powered by the same type of power produced by batteries, which work by generating a voltage at a constant level by means of a controlled chemical reaction. This type of power is known as Direct Current (DC) and is different from the type of power that is supplied to the homes and businesses by electricity suppliers. The type of power supplied to home and business is called Alternating Current (AC). The difference between AC and DC power is that with AC the voltage constantly varies. In order for a computer system to receive the correct type of power and voltage it must be changed from AC to DC by the computer’s power supply.

**Alternating Current**

The mains supply provided by the electricity companies to homes is 220 volts, 13 amps. This means that the available voltage for electrical items in a house, such as a computer or a TV is 220 volts. The electrical plug attached to electrical items must use the correctly rated fuse. Each item has its own rating and common ratings are 3, 5, and 13 amps. Therefore, the maximum amount of current that an item can tolerate is based around the fuse. The fuse is thus a critical safety mechanism for electrical devices. The measure of electrical current is known as amps.

All electrical equipment contains a certain amount of resistance, whether it is wanted or not. This resistance is measured in Ohms, and the relationship between voltage, current and resistance is calculated and expressed in Ohm’s Law.

To confuse the matter further, the domestic electricity supply has another component to it, which is called frequency. The electricity supply at home has a frequency of 50 hertz (Hz).

The four components of an AC electricity supply:

- Voltage (V), measured in volts (v)
- Current (I), measured in amps (A)
- Resistance measured in Ohms
- Frequency (f), measured in hertz (Hz)

Click here to read about the difference between AC and DC and to see an animation that shows both types in action.

Click on this link to have a go at the Science Vocabulary Hangman on energy terminology.