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 currentpotential difference graphs. The filament lamp does not follow Ohm's Law. The resistance of thermistors depends upon the temperature, and the resistance of lightdependent resistors (LDRs) depends upon the light intensity. These components are useful for controlling electrical devices. Circuit symbols
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science ]
