We do experiments so that we can prove one thing affects another. The idea that one variable is the cause and one is the effect of changing the other is called causality.
In experiments, we change the independent variable, we measure the dependent variable and we keep all other variables exactly the same. We do this to be certain that only the independent variable affects the dependent variable when you measure it. In primary school you will have called this conducting a fair test. At LNS we call this Establishing Causality.
When planning an experiment you must fully justify the need to keep control variables constant for an experiment you are planning. To do this work through the following
- Name all variables that must be controlled
- Explain why each needs to be controlled by describing exactly what effect this variable could have on your dependent variable
- Explain how you will ensure this is kept completely constant
The pieces of apparatus you use, environment, chemicals and measuring tools you use could appear in this piece. Remember, you will require accurate equipment and methods in order to establish cause and effect.