Required Practical 15: Resistance

About this practical...

Here you need to find out how resistance changes in circuits. Use this opportunity to put theory into practice as it is an excellent way to find out these relationships yourself. You will find out how the resistance of a wire changes if it gets longer and how resistance changes in series and parallel circuits. (You don?t need to calculate the resistance in a parallel circuit, but you need to see its effect).


1. Collect all of the apparatus needed to set up the circuit shown. Ensure that the power supply is on 2V, the ammeter is in series and the voltmeter is in parallel.

2. Attach the crocodile clips to the thin wire 10cm apart.

3. Turn on the power supply, read and record the voltage and current then turn of the power immediately. (When the current flows, heat is generated and this changes the resistance. It is important that the only variable changing is the length of the wire.)

4. Attach the crocodile clips 20cm apart and repeat step 3.

5. Continue until you have reached 100cm.

Use the results from your table to calculate the resistance at each length - resistance = voltage/current

Plot a graph of Length (x-axis) against Resistance (y-axis).

While you still have the equipment out, repeat any results that are anomalous.

Safety & Managing Risks

Usual lab rules must be followed: Bags and stools tucked away and notify the teacher of any breakages immediately. Take care with sources of electricity. The wires will become hot if you create a short circuit so follow the circuit diagrams carefully. The thin wire may become hot, do not leave the circuit switched on longer than needed to establish a reading. For more detailed information, please consult CLEAPSS.

Technician notes:

Powerpacks (limited to 6V)



Crocodile clips


Long thin resistance wire mounted on a metre rule

This page was updated on: 8th January 2022