If a lighted candle is placed inside a gas jar, everyone knows that it will go out

What happens if two or more candles are placed inside?

This experiment should take around one hour. 


Materials per group

  • Candles of various sizes and of different types
  • Matches

Equipment per group

  • Heat-resistant mats
  • Gas jars
  • Safety glasses

Health, safety and technical notes

  • Read our standard health and safety guidance here. 
  • Wear eye protection and clothing protection, if desired. 
  • Keep away from flammable/combustible materials.
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.


This activity is designed to encourage students to take a logical approach in solving a problem with many variables. The brief is to find out what happens when two or more candles are put in a gas jar. After initial investigation, the student should realise that the height of the candle, the type of wick and the type of wax may all influence the results. Therefore, a proper conclusion can only be drawn if all the variables, except the one under test, are kept constant. Remember to remind students to check for air leaks and mechanical flaws in the apparatus.

Results show that if two or more similar candles of different heights are used, the tallest one will go out first. If two candles of the same height, but different wick thicknesses, are used, the candle with the thinnest wick goes out first. The type of candle wax is also a factor.

The scientific explanation for these results is unknown.


This activity has been extended to include three candles of different heights. It was consistent results, but we don’t understand why.


This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.