State four other pieces of circuit equipment the student needs to carry out this investigation (excluding the components themselves and basic connecting wires).

During the investigation, the student must keep both nichrome wires at a constant temperature.

Give a reason why the wires must be kept at a constant temperature.

Describe two practical methods the student could use to keep the temperature of the wires constant during the experiment.

Four different current–voltage ($I$–$V$) graphs are described below. Match each component to its correct graph description:

• Graph W: A straight line passing through the origin with a very steep positive gradient.
• Graph X: A straight line passing through the origin with a shallow positive gradient.
• Graph Y: A curve passing through the origin that gets less steep (shallower gradient) at higher voltages in both directions.
• Graph Z: Zero current for all negative voltages and small positive voltages, followed by a sharp, near-vertical increase in current at a specific positive threshold voltage.