current and voltage

Current-Voltage relationships

In this experiment the resistance of a lamp, resistor or diode is measured as the current is varied. Voltage and current sensors make the measurements while the software plots the results in real-time. After the experiment, the resistance and the power can be plotted against the potential difference.


Rheostat, dry-cells, lamp, Si / Ge diodes, resistors (e.g. 18 and 36 ohm), interface, voltage and current sensors.

Setting up

If the sensors are adjustable, set a 1A range on the current sensor and a 2V range on the voltage sensor. Some systems recognise the sensors you attach automatically, in others you do this yourself.

You might get the software to plot the following as the experiment proceeds rather than afterwards:

  • the current against potential difference.
  • the resistance (V / I) against potential difference.
  • the power (V x I) against potential difference.

Recording the data

Note that you will not be recording against time, you record one variable against another.

Start recording. Move the rheostat slider to change the current in small steps. Get the software to plot a reading at each step. If no points can be seen, your readings may be out of range – in fact a test run, to check this, is recommended anyway.

Using the results

What does the graph tell you about the change in current?

What does the graph tell you about the change in potential difference?

What is the relationship between current and potential difference?

Use the software to calculate the resistance (V / I). Try to plot resistance against potential difference.

Use the software to calculate power (V x I). Try to plot this against potential difference.

Save your data on disk. Print the graphs.

Alternative using e.g. Pasco Datastudio or Softlab

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