Note:  Do not rely on this information. It is very old.

Frequency

Frequency of any periodic motion means the number of periods in unit time. Thus a seconds' pendulum which exhibits a uniform periodic oscillating motion, takes one second to pass from one side to another, or two seconds to complete the cycle of changes in position. It therefore effects half a period per second, and its frequency is said to be . In the case of red light [Colour] the number of oscillations or periods of vibration per second is 4,024 billions, and the frequency rises in the case of violet light to 7,405 billions per second.