### 2.04 Electrical circuits

An electrical circuit is designed to allow electrical current to flow through it. The current flows through conducting wires. These wires are coated with an insulating material to prevent the current flowing through any other conducting materials that the wires may come into contact with. An electrical voltage is applied to the circuit to produce the current. If the voltage is increased more current will flow. The actual amount of current that will flow will depend upon the applied voltage and the resistance of the circuit. The more resistance the circuit has the less current will flow. The wires themselves have very little resistance (and hence are good conductors). Usually components called resistors are placed in the circuit to limit the current. If the current is too high it will heat the wires and may melt the insulation. If the current is high enough the wire itself may melt, in extreme cases (as is the case for fuse wire) the wire is heated so quickly that it is vaporised with a loud bang.

In order to gain a basic understanding of electrical circuits in the next sections we will look at

• Voltage - potential difference
• Resistance
• Electrical energy and heat energy

### Voltage

Consider a simple circuit with the voltage supplied by a battery. The simple explanation of why electricity flows in the circuit is that the negative electrons in the conductor are attracted towards a large positive charge that is created at the positive terminal of the battery.

(also the electrons are repelled by the negative charge at the negative terminal of the battery).