The AC (alternating) current required for operating many electrical appliances is produced by voltage that varies with time. The voltage in a standard electrical outlet varies with time as a sine function with the frequency f = 120 Hz. This means that voltage goes through 120 cycles (minimum from maximum and then back) in 1 second. The period of the sine function, T, is the time it takes for it to go through one cycle, or from one maximum to another. Period is the reciprocal of frequency:
`T = 1/(f) = 1/(120 Hz) = .0083 ` seconds.
The time required for one cycle is approximately 0.0083 seconds.