Circuits

• Outline the basic steps of the resistance practical.

  1. Set up a circuit with a voltmeter attached in parallel to a resistor and an ammeter attached in series to the resistor.
  2. Start of a low voltage and slowly increase the voltage, recording the potential difference and current values each time, repeat, swapping the resistor for a filament lamp.
  3. Plot a graph of current against potential difference for both components.
• What component is required to alter potential difference if you’re not using a variable power pack?

  A rheostat, or variable resistor
• What is an ‘Ohmic Conductor’?

  A conductor for which current and potential difference are directly proportional, resistance remains constant as current changes, temperature must be constant.
• What must be kept constant to get reliable results?

  Temperature should remain constant so that the resistance of the components isn‘t affected. You should disconnect the supply when not taking readings to avoid unnecessary heating.
• How does temperature affect resistance?

  It causes an increase.
• How do you determine the resistance of a component from an I-V graph?

  The resistance at a given point is the inverse of the gradient of the line drawn from that point to the origin.
• What would you expect the equation for an I-V graph of a fixed resistor to be?

  y = x
• What would you expect the I-V graph of a filament lamp to look like?

  y = x with plateaus at either end
• What happens to the resistance of a filament lamp as the temperature increases?

  Resistance increases. Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow.
• Outline the basic steps of the testing series and parallel circuits?

  1. Set up a circuit with two filament lamps in series, each with a voltmeter attached over them and an ammeter in series with them.
  2. Start on a low voltage and slowly increase the voltage, recording the potential difference and current values each time.
  3. Set up a second circuit with two lamps in parallel and once again record the potential difference and current values for increasing voltages, compare the two arrangements.
• Which lamp arrangement would you expect to have the greatest total resistance?

  The two lamps in series will have a greater total resistance than the two lamps in parallel.
• How would the total resistance of the parallel combination compare to the lamps’ individual resitances?

  The total resistance will be smaller than the smallest individual resistance.
• What safety precautions should be taken when using filament bulbs?

  Avoid touching them when switched on since they can get very hot, be careful not to use too high a voltage to avoid blowing the filament.