How do you calculate the wavelength of radiation?

Answer

That depends on your source.

For any wave phenomenon, the product of the frequency and the wavelength must be equal to the speed of the wave (for stationary source, receiver and medium). This is because frequency is actually the number of wave maxima per unit time that the observer is observing. The longer the wavelength, the further apart two successive maxima are and the longer it takes the observer to observe the next maximum.

See: http://micro.magnet.fsu.edu/primer/java/wavebasics/index.htmlhttp://www.ebaumsworld.com/video/watch/355326/

Let’s take the example of acoustic waves. Some sources will select a fixed wavelength. This is the case with musical instruments, where the length of the instrument determines the wavelength and, through the speed of sound, will determine the perceived frequency. This implies that if you fill a wind instrument with helium (which has a speed of sound about 3 times greater than that of air), it will produce the same wavelength (it is the same length, after all), but the frequency corresponding to this is three times higher.

See: http://www.ebaumsworld.com/video/watch/355326/

Some sources select a frequency or range of frequencies. Typically something that periodically taps against the surface, for example. In that case you calculate the wave length(s) with the above relation.