Current is measured in amps (A), using an ammeter in series. Voltage is measured in volts (V), using a voltmeter in parallel. There is a relationship between voltage, current and resistance (voltage = current × resistance).
The resistance in a circuit can be increased by adding more components, such as resistors and lamps.
Resistance is measured in ohms.
It can be calculated from the potential difference across a component and the current flowing through it.
The total resistance of a series circuit is the sum of the resistances of the components in the circuit.
Resistors, filament lamps and diodes produce different current-potential difference graphs.
The filament lamp does not follow Ohm's Law.
The resistance of thermistors depends upon the temperature, and the resistance of light-dependent resistors (LDRs) depends upon the light intensity. These components are useful for controlling electrical devices.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science ]