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In Science we often talk about controlled experiments and the control in an experiment. What do these terms mean?

Controlled variables

A controlled experiment has controlled variables. This means that all variables, except the one variable that you are changing, are kept the same.

In the experiments with the UV beads we control the following variables.


Should all the beads be the same colour?

  • do the different coloured beads change at different rates?


Should the amount of sunlight be the same?

  • does being in the shade affect the result?


Should the temperature be the same?

  • does temperature have an effect on the result?


Should the container be the same?

  • does it matter what size the container is?

All of these factors have to be thought about and decided on when planning the experiment.

The control

A control makes sure that the experiment is valid. It has all the same variables as the experiment but not the one variable that you are changing. This means that any differences in results can be because of the one variable that is different.

For example, if you wanted to test the effect of sunglasses on the amount of ultraviolet radiation getting through. You would have a control that had all the same conditions except the sunglass lens. If the beads are different colours we can confidently say that the effect was caused by the sunglasses.

Two containers with beads, one covered with a sunglass lens.

The control on the left has the same number and colour of beads and the same container, the difference is that one is covered with a sunglass lens