A control experiment in which the desired outcome is no effect
Example 1: You set up an experiment where you are testing to see if two reagents interact. A simple negative control would be to use just one reagent and some water in place of the other to see if something happens. IT SHOULD NOT IN THE CONTROL. If it does then there is something wrong and likey to be contamination.
Positive Control
A control experiment in which the desired outcome is a well-defined/well-known effect
A positive control is used in experiments to demonstrate that the scientist and her/his laboratory are capable of carrying out the experimental design.
