Here's an interesting question from my graduate course. Suppose electromagnetic radiation propagates though a neutral dielectric in a region of normal dispersion. The medium has a refractive index n. Let s be the signal that first arrives at point x within the medium. At what velocity does s propagate? Answer in terms of the speed of light in a vacuum, c.
Surprisingly and yet unsurprisingly, this is false. I'd recommend thinking more about the physics of the actual situation described, rather than equations and definitions.
- Is this just simply...
Surprisingly and yet unsurprisingly, this is false. I'd recommend thinking more about the physics of the actual situation described, rather than equations and definitions.
- Is this just simply...
Edit: the answer isn't immediately obvious (until you know it, then it is) so I feel like this question deserves some hints. I'll give them in terms of questions to guide thinking.
1) What causes light to slow down in a dielectric medium in the first place?
2) Why does it matter if the medium is neutral?
3) What exactly is a signal?
4) What significance does being the first signal to arrive at x have?
The purpose for my questions is not necessarily to just answer my question, but to give deeper insight into the physics of the problem, and a way to approach physics and the sciences in general. I think Science Olympiad does a good job in introducing students to a wide variety of subjects, but due to its competitive nature can neglect understanding and deeper insight into the concepts. Hope this helps!
The answer is correct but the reasoning is not. It's unlikely that this will be answered completely correctly anytime soon so I'll let you go.
- Okay. After thinking a while, I think I have some idea.
Okay thanks. Now I have one. The image below shows the absorption coefficient of water as a function of photon wavelength. Now, imagine sunlight hitting the surface of a lake. Determine the ratio between intensities of red light of wavelength 670 nm and blue light of wavelength 475 nm 2 meters below the surface.The answer is correct but the reasoning is not. It's unlikely that this will be answered completely correctly anytime soon so I'll let you go.
- For the actual answer
Is that only for pulsed light (impulses), or is it true for monochromatic continuous wave light as well? You're original question did not specify. An impulse (or pulse) has many frequencies in it.The answer is correct but the reasoning is not. It's unlikely that this will be answered completely correctly anytime soon so I'll let you go.
- Okay. After thinking a while, I think I have some idea.
- For the actual answer
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