Required practical

Factors that affect resistance

There are different ways to investigate the factors that affect resistance. In this required practical activity, it is important to:

  • record the length of the wire accurately
  • measure and observe the potential difference and current
  • use appropriate apparatus and methods to measure current and potential difference to work out the resistance
Circuit with a 1.5 V cell, ammeter, voltmeter and thin resistance wire connected in parallel. Length of wire is measured using a meter ruler.

Aim:

To investigate how changing the length of the wire affects its resistance.

Method:

  1. Connect the circuit as shown in the diagram above.
  2. Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
  3. Record the reading on the ammeter and on the voltmeter.
  4. Move one of the crocodile clips closer until they are 90 cm apart.
  5. Record the new readings on the ammeter and the voltmeter.
  6. Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
  7. Use the results to calculate the resistance of each length of wire by using \text{R} = \frac{\text{V}}{\text{I}}, where \text{R} is resistance, \text{V} is voltage and \text{I} is current.
  8. Plot a graph of resistance against length for the resistance wire.

Results:

Some example results may be:

Length (cm)Potential difference (V)Current (A)Resistance (Ω)
1001.200.167.5
901.180.176.8
801.000.175.9
700.960.185.3
600.930.214.4
500.890.253.6
400.840.273.1
300.750.312.4
200.630.441.4
100.410.630.7

Analysis:

Graph plotting length against resistance, line of best fit shows a direct positive correlation.

Evaluation:

From the graph it can be seen that the longer the piece of wire, the higher the resistance, and that resistance is directly proportional to length as the graph gives a straight line through the origin.

Hazards and control measures

HazardConsequenceControl Measures
Heating of the resistance wireBurns to the skinDo not touch the resistance wire whilst the circuit is connected and allow time for the wire to cool.