Why is wavelength important than frequency ?
Whenever you see physicists talking about light, you might have noticed they prefer to use wavelength of the light rather than it’s frequency.
This is not a slip of the tongue and there is a very simple reason to it.
It is convenient to measure the wavelength of light experimentally rather than its frequency.
Take the violet light of wavelength 400nm. If we calculate it’s frequency, it turns out to be:
Can’t we measure 7.5 x 10^14 Hz directly ?* There is a theorem by Nyquist in signal processing which states that:
The minimum rate at which a signal can be sampled without introducing errors, is twice the highest frequency present in the signal.
This means that if you want to measure the frequency of light accurately then you need to be sampling at 2*(7.5 x 10^14) Hz in order to measure it and this is incredibly hard to achieve this instrumentally!
On the other hand, here is how easy it is to measure the wavelength of the light:
Take the source of light and pass it through a diffraction grating.
Measure the angle(theta) between the highest intensity (zero order) and say the ‘nth’ order. (see diagram above).
Use the following formula for the wavelength : **
where, d - distance between the slits (will be provided by manufacturer of diffraction slit), n - order of the slit, theta- from measurement.
And voila, you have the wavelength of the light. That’s how simple it is to get the wavelength of a source light. Since speed of light is a constant, the frequency of light is found out from the following relation:
In addition to this, you can also derive the energy of a photon using the relation:
And so on and so forth. All of these following from a simple diffraction experiment! That’s why calculating the wavelength of light is so crucial.
* There are some indirect means to do this. Check this physicsforum page for more.
** How do diffraction gratings work ?
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