How many variables can be tested at the same time in an experiment?

Question

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Answer 1

According to the Scientific Method --- ONE.

The only way to test a particular variable for sure is to leave all other variables constant, and if a change in ONE variable creates an overall change, then you know that that variable caused it. But if you change 2 variables, and something changes, you don't know which one changed it for sure.

So, one variable at a time. A full experiment can test many variables, though.

Answer 2

You can have many variables in an experiment but at the simple GCSE level you need to control all but one variable so that a simple graph can be drawn.

Answer 3

better just to test one variable at a time that way one knows that any changes observed are accounted for by that variable.