Speed of an EM wave

c=\lambda f

Result unit: m/s

What it describes

An electromagnetic wave in vacuum travels at the speed of light — the product of the wavelength and the frequency.

c

speed of light (

\approx 3\cdot10^{8}

)

[m/s]

\lambda

wavelength

[m]

f

frequency

[Hz]

All EM waves in vacuum travel at the speed of light

c\approx3\cdot10^{8}

m/s. That is why shorter waves (e.g. gamma rays) have a higher frequency.

Radio waves, light, radiation; the relation between

\lambda

and

f

A radio wave has

f=100

MHz. Calculate the wavelength.

Substitution

c=3\cdot10^{8}

f=10^{8}

Result

\lambda=\dfrac{3\cdot10^{8}}{10^{8}}=3

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