A student measures the time for ten oscillations of pendulums of different lengths. Which is the independent variable?

Correct answer: Length of pendulum

Direct answer: Option A is correct. In this experiment, pendulums of different lengths are compared, so length is the factor deliberately changed. That makes pendulum length the independent variable. The time for ten oscillations is measured and is therefore the dependent variable. Option A works because changing length is the planned input of the investigation. Option B is wrong because measured time is the response or outcome. Option C is wrong in the usual fair-test design because the bob’s mass should be kept the same, making it a controlled variable rather than the independent one. Option D is wrong because the number of oscillations is fixed at ten in every trial; a fixed condition is controlled, not independent. The reasoning is: keep the bob and procedure comparable; change length; measure ten-oscillation time; compare times. A longer or shorter pendulum may produce a different time, but the experiment can test that only when length is the intended change. Memory cue: the factor described as “different” is often the independent variable.