combustion – burning a candle

As a candle burns oxygen is used and heat and water are produced. A few sensors can be used to monitor this process. A light sensor indicates when the candle is extinguished, a humidity sensor measures the water produced while an oxygen sensor monitors the oxygen level.

what you need

Candle, bell jar, matches, interface and temperature, light, oxygen and humidity sensors.

setting up

Set up the candle and sensors inside the bell jar and arrange them so that the probes will be well away from the candle flame.
Connect the sensors to the interface. Allow an oxygen sensor time to stabilise. Some systems recognise the sensors you attach automatically, in others you do this yourself.
Record for 3 minutes. Light the candle, cover it with the bell jar. When the candle has extinguished, readmit air into the bell jar.


  • How does the graph show you the candle produces heat?
  • How does the graph show you the candle produces water?
  • How does the graph show you the candle produces light?
  • How does the graph show you the candle uses oxygen?
  • When is the oxygen level at its lowest?
  • Why does the oxygen level increase at the end?
  • How important do you think it is to calibrate the oxygen sensor to read in absolute units?

Activities in this section adapted from The IT in Science book of Data logging and Control. © IT in Science and may be reproduced as needed for use within school.

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