required practical 3

• Factors affecting the resistance of electrical circuits

  • Length of a wire
• Equipment used


  • Battery
  • Ammeter
  • Voltmeter
  • Length of wire
• Measuring resistance in the circuit

  1. Use ammeter to measure current

  2. Use voltmeter to measure potential difference

  3. Calculate resistance using R=V/I
• Increasing length of wire

  Increases resistance
• Zero error


  A reading on a measuring instrument when the value should be zero (a systematic error)
• Zero error is caused by the equipment, e.g. difficulty getting crocodile clip at zero position, resistance from contact between clip and wire
• Zero error needs to be subtracted from all resistance readings
• Heating effects


  As temperature of wire increases, resistance also increases
• Reducing heating effects


  1. Use low potential difference to keep current low

  2. Only turn on current when taking readings, turn off between readings
• Variable resistor


  Contains a long piece of wire in a coil, using a slider to change the length of wire the current runs through
• Variable resistors are used to control potential difference across a component