Often it is necessary to measure the rate at which objects rotate. An instrument which is capable of doing this is called a stroboscope.
Stroboscopes give flashes of bright light.
This light is then made to fall on the rotating object. The rate at which the stroboscope flashes light is then adjusted so that the light falling on the rotating object appears to be stationery. At this point of time the frequency of flashing of the stroboscope is the same as that of rotation of the object. In this way the rate of rotation of rotating objects can be determined. Let us now undertake a simple experiment to demonstrate this concept.