GCSE Physics Required Practical

Investigating how the Resistance of a wire varies with its length

A dimmer switch allows you to control the brightness of a lamp. You will investigate how the dimmer switch works. You will construct a circuit to measure potential difference across a wire and the current in the wire. You will also do that for different lengths of wire.

Apparatus

  • Power supply
  • Ammeter
  • Voltmeter
  • Crocodile clips
  • 1 Metre of constantan wire
  • Metre Ruler
  • Connecting leads

Method

  1. Connect the circuit with the power pack set t 4 Volts or a battery pack set to 4.5 Volts
  2. Use tape to secure the wire to a metre rule and connect 100cm of the wire in the circuit
  3. Record in a table:
  • The length of the wire between the crocodile clips
  • The current
  • The potential difference

  

  1. Calculate ad record the resistance in the table using the equation Resistance=potential difference/current
  2. Move the crocodile clip to 90cm and record the new ammeter and voltmeter readings - the potential difference may not change
  3. Repeat this shortening the wire by 10cm each time - Do not allow the ammeter reading to exceed 3Amps
  4. Tidy away apparatus
  5. Plot a line graph with Resistance in Ohms on the y-axis and length of wire on the x-axis
  6. Add a line of best fit to the graph