what is the si unit for frequency
This period is the reciprocal of the frequency. This is written as: T = 1/f. where T is the period and f is the frequency. The SI unit for frequency is the hertz (Hz), which is equal to 1/s, or once per second. Frequency is encountered many times in physics. A few highly important instances are listed here. All waves in physics are said to have frequency.
This is consistent with frequency defined as revolutions per second in a mechanical context, or cycles per second in an electrical context, and lets you write frequency-dependent equations without requiring the 2*pi conversion factor. In the SI unit system, however, the unit of frequency is hertz (Hz), defined as 1/s.