Year 8 Voltage & Current Investigation – Teacher Support Notes

Pupils are investigating how the current through a piece of Nickel-Chrome wire changes as the length of the wire is changed. The focus of the module is preliminary work, so pupils are expected to establish the range and values of the main variables independently. These notes provide advice and information for non-specialists to help guide the pupils in the right direction, and ensure safe working practice.

Overview of Practical Task:

Pupils will apply a small voltage across varying lengths of Nichrome wire, causing a current to flow. The magnitude of this current depends on the voltage applied and the length of the wire.

Safety Note:

If an excessively large current is allowed to flow the wire can become extremely hot presenting a hazard to pupils. The values of voltage and lengths of wire must be kept within safe ranges to prevent this.

  • pupils should use one cell to power their circuit and NOT power packs
  • the minimum length of wire pupils can test is 10 cm

Using these values the current will not exceed around 0.6 Amps. The wire will get warm but not sufficiently to present a hazard.

Suggested method (this is what you should be guiding pupils towards!):

Use sticky-tape to secure a metre length of Nichrome wire a metre ruler. Attach a crocodile clip to each end. Connect a cell across the wire, and include an ammeter to measure the current. Your circuit should be one big ‘loop’ at the moment, with the ammeter connected in the loop. Now connect a multimeter across the cell, to measure the voltage (use the bottom two holes on the multimeter, and the 20V D.C. range, 3 clicks anticlockwise from the ‘off’ position).

Now you can move one of the crocodile clips to adjust the length of wire in the circuit. The current should change (shorter length = bigger current). Measure the current for a number of lengths (e.g. 10cm, 20cm, 30cm etc up to 1m) and record the results in a table.

Voila – you have your results! You can now plot a graph of Current (on the y-axis) against Length of wire (on the x-axis) to determine what kind of relationship you have!