What Are Frequency and Period? (Hz)

Frequency shows how many times per second a repeating (periodic) signal repeats; its unit is the hertz (Hz). The period is the duration of one full cycle of that signal. Both are fundamental concepts for alternating current (AC) and all signals.

What Is Frequency? (Hz)

1 Hz means one full cycle per second. For example, the mains voltage in many countries is 50 Hz (60 Hz in North America); that is, it changes direction 50 times per second. Audio, radio and clock signals work at much higher frequencies.

What Is the Period?

The period (T) is the time it takes to complete one cycle, usually measured in seconds (s) or milliseconds (ms). As frequency rises, the period shortens.

The Frequency-Period Relationship: f = 1/T

The two are inverses of each other: f = 1 / T and T = 1 / f.

Where Does It Come Up?

Frequency comes up in audio systems, radio communication, processor speed (clock frequency) and PWM signals. Crystal and oscillator components are used to produce a stable frequency.

Common Mistakes

• Mixing up unit multiples: 1 MHz = 1000 kHz = 1,000,000 Hz; the calculation is wrong without converting.
• Skipping the period unit: in f = 1/T, T must be in seconds; putting it in ms throws the result off by 1000×.
• Confusing frequency with amplitude: frequency is the rate/repetition; amplitude is the size of the signal.