Wave speed, frequency and wavelength — Physical education, 14–17 years
Waves transfer energy and information without carrying the material along with them overall. Three measurements describe their repeating pattern: speed, frequency and wavelength.
The idea
A wave is a repeating disturbance that travels. Frequency is how many complete waves pass a point each second; wavelength is the distance from one matching point to the next. Their link is wave speed = frequency × wavelength, v = fλ.
Why it matters
People needed one way to compare ripples, sound and light, even though these waves look very different. The relationship v = fλ explains why, in the same medium, a higher frequency means a shorter wavelength: the same distance is filled with more wave cycles.
A worked example
A sound wave travels through air at 340 m/s and has a frequency of 680 Hz. Start with v = fλ, then rearrange to λ = v/f. Substitute the values: λ = 340 ÷ 680 = 0.50 m. Each wave cycle is therefore half a metre long.
The common trap
A reasonable mistake is to say that a louder sound has a higher frequency. Loudness depends mainly on amplitude, the size of the vibration; frequency sets the pitch. The words feel linked because a strong vibration can make a sound seem more noticeable, but they measure different things.
Outside school
Radio stations use different frequencies so their signals can be separated. Doctors use ultrasound waves to make images inside the body, and musicians choose notes with particular frequencies. In each case, wave speed, frequency and wavelength help describe what is sent and detected.
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