An experiment is designed to test what color of light will activate a photoelectric cell the best. the photocell is set in a circuit that "clicks" in response to current. the faster the current, the more clicks per minute. in this experiment, the number of clicks in one minute is recorded for each color of light shining on the photocell. to change the color of light, a different color of cellophane is placed over the same flashlight and the flashlight is then located a specific distance from the photocell.
in the above experiment, which factor is the independent variable?

the color of light shining on the photocell.

Explanation:

1) In an experiment there are two kind of variables: independent variables and dependent variables.

2) The independent variable is the one that can be changed or manipulated. This is done because you want to learn how the changes in this variable may explain or are related to other variable (the dependent variable).

In the description of the experiment, the color of the light is being changed, by placing different color of cellophanes ove the same flashlight.

This is how, keeping the control over other possible variables (the flashlight kind and its distance from the photocell, for example) the experimenter manages to change one only variable: the color of light.

3) On the other hand, the dependent variable, is the variable that is being explained. You do not manipulate the dependent variable directly but you want to learn to what extent this dependent variable is determined by, explained by, predicted by, or simply related to, the independent variable.

In conclusion, the independent variable is the color of light.

the correct answer is:

a. formation of precipitation