Question

1. A 3 bladed fan is spinning at 16.7 revs/sec in a very dark room. If a flashing light (called a strobe light) flashes at just the right frequency, the spinning blades look motionless. What is the shortest time, in seconds, between flashes that will make the fan appear to be stopped?

Answer 1

P = 1 / f = 1 / 16.7 = .06 sec period of 1 revolution

Period of 1/3 revolution = .06 s / 3 = .02 sec

If the light flashes every .02 sec the fan will appear motionless