Key learning points

1. An appropriate range of p.d. values includes 0 V and the maximum p.d. of the lamp and at least four other readings.
2. For electricity investigations, it is good practice to take many more than the minimum number of measurements.
3. After plotting a graph, extra readings could be taken to fill gaps or to check possible errors.
4. Plots that lie off the best fit line are possible errors that need to be checked.
5. The resistance of a filament lamp is calculated from an I–V graph using pairs of readings and the equation R = V ÷ I.

Keywords

• Filament lamp - a type of lamp that uses a hot wire to emit light

• Variable resistor - a resistor that can be easily changed to any value in its range

• Range - the minimum to maximum possible values in an experiment

• Repeat reading - when a measurement is taken again to improve the experiment

• Best fit line - a line that shows the underlying trend of a set of results on a graph, it can be straight or curved

Common misconception