Final answer:
Before using a rotameter to measure an unknown flow rate, a calibration curve is needed. The calibration curve is created by plotting the flow rate of known volumes of fluid against the position of the float in the rotameter. This curve can then be used to determine the flow rate of an unknown fluid based on the position of the float.
Step-by-step explanation:
Before a rotameter can be used to measure an unknown flow rate, a calibration curve is required.
A rotameter is a device used to measure the flow rate of a fluid. It consists of a tapered tube and a float. As the fluid flows through the tube, the float moves up or down, indicating the flow rate.
The calibration curve is obtained by measuring the flow rate of known volumes of fluid and recording the corresponding position of the float. By plotting these data points on a graph, a calibration curve can be created, which can then be used to determine the flow rate of an unknown fluid based on the position of the float.