How to Calculate Periodicity

Periodicity may be generally defined as the length of time required to complete an event. It implies that the event is occurring repeatedly and requires the same length of time to complete each time. We therefore use periodicity most often to describe cyclic phenomena such as light waves, sound waves and voltage for alternating current. Periodicity is closely linked to frequency and may be calculated directly from the frequency.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Calculator

The Steps

1. Define frequency and periodicity more formally. Frequency is the number of cyclic events (cycles) that occur in a given period of time. Periodicity is the amount of time that a cycle requires to complete and is therefore the reciprocal function of frequency.

2. Define the units of measure for periodicity. Frequency is measured in cycles per unit time and the standard unit of measure is the hertz, which is defined as 1 cycle per second. The standard unit of measure for periodicity is inverse hertz (Hz^-1) since periodicity is the reciprocal of frequency,

3. Calculate the period from the frequency with the equation T = 1/f where T is the period and f is the frequency. For example, the frequency of household voltage is 60 Hz so its period is 1/60 Hz^-1.

4. Interpret the results in the previous step: 1/60 is about 0.0167, so household voltage requires about 0.0167 seconds to complete a cycle.

5. Find the periodicity of light waves. The frequency of light waves is given as f = c/Y where c is the speed of light and Y is the wavelength of the light. The period T of a light wave is therefore given by T = Y/c.

References

• University of Utah

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