Resistance

• Investigating factors affecting resistance of electrical circuits

  1. Use battery, ammeter, voltmeter, and wire

  2. Measure current and potential difference

  3. Calculate resistance using formula: R = V/I

  4. Vary length of wire

  5. Plot graph of resistance vs length
• Graph shows a straight line passing through zero, indicating resistance is directly proportional to length
• Zero error


  A reading on a measuring instrument when the value should be zero, a systematic error
• Zero error is caused by difficulty in positioning crocodile clips at zero on ruler, and resistance from contact between clips and wire
• As temperature of wire increases

  Resistance also increases
• Reducing heating effects


  • Use low potential difference to keep current low
  • 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 lamp, increasing resistance dims the lamp