Plan an experiment to investigate the relationship between the length of a wire and its electrical resistance.

Resistance is calculated using the equation $R=\frac{V}{I}$.

The following apparatus is available:

• ammeter
• voltmeter
• d.c. power supply
• metre rule
• a long constantan (resistance) wire taped to a ruler
• connecting leads and crocodile clips

You can also use other apparatus and materials that are usually available in a school laboratory.

In your plan, you should:

• draw a diagram of a suitable electrical circuit using standard electrical symbols
• explain briefly how to carry out the investigation, including how to measure different lengths and how to obtain the measurements needed to calculate resistance
• state the key variables to keep constant to ensure a fair test
• draw a table, with column headings and units, to show how to display your readings (you are not required to enter any readings in the table).