Period is the time for one complete wave cycle. It is measured in seconds. A wave with a period of 0.01 seconds completes one cycle in that time. Period is the reciprocal of frequency. If the frequency is 100 Hz, the period is 0.01 seconds. If the period is 2 seconds, the frequency is 0.5 Hz. The relationship is simple: T = 1/f. Period is used for all types of waves, including sound, light, and water waves. It is also used for any repeating phenomenon, like the swing of a pendulum or the orbit of a planet.

The period of a pendulum depends on its length and the acceleration due to gravity. A longer pendulum has a longer period. The period does not depend on the mass of the pendulum bob or the amplitude of the swing, at least for small amplitudes. That discovery, made by Galileo, led to the development of pendulum clocks. The period of a wave is related to its wavelength and speed by the equation v = λ/T, where v is wave speed, λ is wavelength, and T is period. Period is a useful concept because it describes how long a repeating event takes, which is often more intuitive than frequency.

Period facts

• Definition. Time for one complete cycle.
• Unit. Second (s).
• Reciprocal. T = 1/f.
• Pendulum. Depends on length and gravity.
• Wave. v = λ/T.

Period is not the same as frequency. Period is the time for one cycle. Frequency is the number of cycles per second.