Engineers connect components in electrical circuits in series or parallel to make a range of useful circuits. We can calculate the voltage, current and resistance in these circuits.

The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it and produces light as a result.

Taking corresponding pairs of values for V and I from the graph at different voltages will give different values of resistance. The resistance will be higher at higher voltages.

The filament lamp does not follow Ohm's Law. Its resistance increases as the temperature of its filament increases. So the current flowing through a filament lamp is not directly proportional to the voltage across it.

Diodes are electronic components that can be used to regulate the voltage in circuits and to make logic gates. Light-emitting diodes (LEDs) give off light and are often used for indicator lights in electrical equipment such as computers and television sets.

You should be able to recognise the graph of current against voltage for a diode.

The diode has a very high resistance in one direction. This means that current can only flow in the other direction. This is the graph of current against voltage for a diode. Normally a diode will not conduct until a particular voltage is reached.