What is an control variable and give examples.?

Answer 1

Experimental design and data analysis
In the design of experiments and data analysis, control variables are those variables that are not changed throughout the trials in an experiment because the experimenter is not interested in the effect of that variable being changed for that particular experiment. (In other words, control variables are extraneous factors, possibly affecting the experiment, that are kept constant so as to minimize their effects on the outcome.) An example of a control variable in an experiment might be keeping the pressure constant in an experiment designed to test the effects of temperature on bacterial growth.

In a scientific experiment, the controlled variable never changes; it is the same for every setup. For example, in an evaporation experiment, the area must be the same.

Control theory
In control theory, control variables are variables that are input to the control system.

Programming
In programming, a control variable is a program variable that is used to regulate the flow of control of the program. For example, a loop control variable is used to regulate the number of times the body of a program loop is executed; it is incremented (or decremented when counting down) each time the loop body is executed.

Answer 2

Hi. When you design an experiment a control variable is one or more in which you have no interest in changing. Like coolant on or off in a machining process. http://en.wikipedia.org/wiki/Control_variable