Exam Question Today

[Phoenix (Steve)]

My two cents worth - I believe Steven has hit the nail on the head here. The lower frequency radio waves have much longer wavelengths than visible light and thus visible light will interact considerably more than radio waves through the same medium. Consequently, the velocity of visible light will be marginally slower (through a vacuum the speed is pretty much the same). I understand this interaction with the atmosphere to be associated with Rayleigh's scattering, Mie scattering and Non-selective scattering of visible light.

Cheers
Steve

[circumpolar (Matt)]

Originally Posted by sjastro

Refraction only occurs at the interface of two mediums. There is no deviation in the medium.

Apart from Raman scattering slowing down visible light more than radio waves, there is another consideration.

Low frequency radio waves have wavelengths in the range of 1000-100,000 km, the troposphere is only about 20 km thick. Only a small percentage of the wavelength actually interacts with the bulk of the atmosphere unlike the wavelength of light.

Regards

Steven

Even though it occurs at the interface, the event causes the beams to take different pathways (vector) through the medium.

Good point regarding the very long radio waves. Once again this demostrates the unspecific nature of the Question.

As a side note, I have since learnt that it is the Frecency that is least affected (if at all) when transitioning through media. That is, the speed is changed (Cm = C / refractive index) and the wavelength (lamda) also changes proportionaly with Cm to concerve the Frequency value.
This way the speed is always equal to the product of Frequency & Wavelength.

[circumpolar (Matt)]

Originally Posted by Phoenix

The lower frequency radio waves have much longer wavelengths than visible light and thus visible light will interact considerably more than radio waves through the same medium. Consequently, the velocity of visible light will be marginally slower (through a vacuum the speed is pretty much the same).

Cheers
Steve

Agree.
That is, When we are talking about velocity I agree.
But remember we are talking about speed here, wich has a specific meaning.

[circumpolar (Matt)]

I should get my exam marks back today, unless there is some sort of teacher strike.

I'm now ready to fight for my interpritation of the question.
Thanks for all your help in nutting this out.
Who knows, I may have given the correct answer after all.

[sjastro]

Originally Posted by circumpolar

Agree.
That is, When we are talking about velocity I agree.
But remember we are talking about speed here, wich has a specific meaning.

Velocity is speed in a particular direction. In reference to your question the terms are interchangeable.

If the question is simply asking is there a difference in the speed (velocity) of light, between light and radio waves in vacuum, and between light and radio waves in air, then refraction, different trajectories in a the medium etc are not relevant.

Seems like the question has been made unnecessarily complicated.

Regards

Steven