A student investigates the relationship between the length and the resistance of a wire.

The following apparatus is available:

• a long constantan wire of uniform diameter, taped to a metre ruler
• ammeter
• voltmeter
• crocodile clips and connecting leads
• power supply.

Other apparatus normally found in a school laboratory is also available.

Plan an experiment to investigate how the length of the wire affects its resistance.

Resistance $R$ is given by the equation $R=\frac{V}{I}$, where $V$ is the potential difference (p.d.) across the wire and $I$ is the current in the wire.

You do not need to write about safety precautions.

In your plan:

• draw a circuit diagram to show the circuit you use
• explain briefly how to do the investigation
• state one key variable to keep constant (other than the material or diameter of the wire)
• draw a table, or tables, with column headings, to display the readings (you are not required to enter any readings in the table)
• explain how to use your results to reach a conclusion.