# What is the the frequency of electromagnetic radiation with a wavelength of 420 nm?

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The frequency and the wavelength of electromagnetic radiation are related by tge following formula:

`lambda = c/f` , where `lambda` is the wavelength, f is the frequency and c is the speed with which the electromagnetic radiation propagates (in a vacuum, or air), also known as the speed of light: `c = 3*10^8 m/s` . From here, the frequency can be expressed as

`f = c/lambda`

The wavelength of 420 nanometers is `420*10^(-9)` in meters, so``

`f = c/lambda = (3*10^8)/(420*10^(-9)) = 7.14*10^14 1/s`

Such electromagnetic radiation is visible light of violet-blue color.

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