# Scientists Say: Frequency

## A wavelength is distance, but the number of wavelengths over time is frequency

#### Frequency (noun, “FREE-kwen-see”)

This is the number of times that a periodic event occurs over a particular unit of time. Periodic events are often waves — such as sound waves— and are measured in wavelengths. The number of wavelengths over time is known as the frequency. But frequency can also be used for other things, such as the number of rotations on a wheel over time. Frequency is measured in hertz — the number of times a cycle repeats per second.

#### In a sentence

A radio telescope identified a certain frequency of radio wave bursts to intelligent life. Unfortunately, that life turned out be us.

### Power Words

frequency  The number of times a specified periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

hertz  The frequency with which something (such as a wavelength) occurs, measured in the number of times the cycle repeats during each second of time.

wavelength  The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

Bethany Brookshire was a longtime staff writer at Science News Explores. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.