Why the frequency of Electromagnetic Wave does not change but its wavelength change, when it undergoes a change in medium of propagation?
Hi Muhammad,
imagine a source of an em wave located in air, and yourself enclosed in a medium with speed of propagation = half the speed in air, counting the passing wave hillocks. To make things simple, the source, you, and the medium are not moving relative to each other. Assume that the frequency of the source is 1 Hz but the frequency of the wave in your medium is only 1/2 Hz. After 10 seconds, the source has released 10 full waves, and you have counted 5. Where are the missing 5? Perhaps somewhere between the source and your location? But after 100 seconds 50 full waves are missing, after 1000 seconds ... obviously this cannot happen - an unlimited number of full waves cannot be stored away in a limited stretch of space, and the waves cannot simply disappear.
So, whatever period of time you are observing, the number of full waves passing you has to be equal to the number of full waves produced by the source. In other words, you observe the same frequency, independent of the medium you are located in.
The shorter wavelength in your medium is a necessary consequence of the unchanged frequency and the lower speed of propagation.
PS. After looking at your profile, I'm a bit confused by the nature of this question and your fluent writing about Tamm waves and Uller-Zenneck waves in your paper "Surface electromagnetic waves propagation guided by dissipative dielectric material sandwich between two periodic multilayered isotropic materials in prism coupled configuration". But ... I have always suspected that STEM university education is squeezed into a way too short period of time (it was for me), and that the average student, after successfully doing the exams, has to work backwards - if time permits - in order to really understand at least the most important basics.
Of course it does. Please see my first answer:
"The shorter wavelength in your medium is a necessary consequence of the unchanged frequency and the lower speed of propagation."
v = 1 / sqrt(epsilon * my) with the permittivity epsilon and the permeability my of the respective medium.
Unchanged frequency and unchanged velocity would result in unchanged wavelength; i.e. for em waves, every medium would behave like vacuum. No optical lenses (no microscope, no telescope, no glasses), no optical prisms (no rainbows), no mirrors etc.
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