IP Current and potential difference graphs © Oxford University Press 2011 Current and potential difference graphs

IP Current and potential difference graphs © Oxford University Press 2011  The relationship between current and potential difference (voltage) in a circuit is an important one.  The relationship was investigated over 200 years ago.  With modern equipment it is very easy to investigate it in the lab.

IP Current and potential difference graphs © Oxford University Press 2011  In this circuit, the link between the potential difference supplied to a lamp and the current through the lamp is being investigated. Various potential differences can be set up. The potential difference is increased simply by turning the knob on the power supply.  The current flowing through the lamp is recorded for each potential difference.  The results can then be plotted on a current–potential difference graph. You can replace the lamp in this circuit with different components and plot the graph of current versus potential difference for each one.

IP Current and potential difference graphs © Oxford University Press 2011  This is the current–potential difference graph for a resistor.  The line passes through the origin and has a constant positive gradient. This shows that the current through the resistor is directly proportional to the potential difference across the resistor. Any change in the potential difference changes the current in the same proportion. The graph for a resistor will only be a straight line if the temperature of the resistor stays the same.