$\dfrac {sin\theta1}{sin\theta2}=\dfrac {v1}{v2}=\dfrac {n2}{n1}$

I understand this equation, but what is the velocity of a light wave going through air and what is the velocity/change in velocity as it enters standard glass of roughly 1.5 refractive index?


closed as too localized by Qmechanic, David Z Mar 16 '12 at 14:15

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    $\begingroup$ What is up with this flood of basic optics questions? Just get a textbook already $\endgroup$ – user2963 Mar 15 '12 at 17:47
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    $\begingroup$ And if you understand that equation, the answer should be obvious. $\endgroup$ – user2963 Mar 15 '12 at 17:47
  • $\begingroup$ What haven't you understood? Ditto zephyr on both counts. $\endgroup$ – Manishearth Mar 15 '12 at 18:14
  • $\begingroup$ I don't know where to get a textbook on this stuff, I don't see why you care anyway, just don't look at the question. I just want to know the velocity of light in air and in glass $\endgroup$ – ODP Mar 15 '12 at 18:25
  • $\begingroup$ @OllyPrice amazon.com/s/… physics.stackexchange.com/questions/21288/… en.wikipedia.org/wiki/Optics $\endgroup$ – Bernhard Mar 15 '12 at 18:29

The answer first: the speed of light and the refractive index are closely related. The speed of light in some material with refractive index $n$ is simply:

$$v = \frac{c}{n}$$

where $c$ is the speed of light in vacuum. The refractive index or air is around 1.0003 - see http://en.wikipedia.org/wiki/Refractive_index for details.

Then some comments: bearing in mind that we all have limited time, it would be worth reading up a bit before posting questions. If you're interested in optics I can recommend the book I learned from, Optics by Hecht and Zajac - http://www.amazon.co.uk/Optics-World-Student-Eugene-Hecht/dp/0201304252 - I learned optics 35 years ago but it hasn't changed much!

  • $\begingroup$ Okay I'll buy that book thanks, I'm 15 so don't really have access to textbooks like 'zephyr' said. And thanks for your ANSWER. $\endgroup$ – ODP Mar 15 '12 at 18:33
  • $\begingroup$ I'm confined to a hospital bed most of my life so library is out of the question, and believe it or not I do look on the internet before posting questions, but looking on the internet for a long time does get tedious when posting on here guarantees a fast answer. $\endgroup$ – ODP Mar 15 '12 at 18:37
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    $\begingroup$ @OllyPrice - I'm sorry to hear that, and I am glad and impressed that you are studying physics at such a young age. However, I don't think this site is meant for basic tutorial questions like these, especially when there is no real conceptual component. Furthermore, I doubt that your learning benefits much from getting answers like this - if you can't apply that equation to answer your own question, you should take a step back. $\endgroup$ – user2963 Mar 15 '12 at 19:42
  • $\begingroup$ What is it about Optics by Hecht that makes it so much more expensive than any other book? I need to know this before I invest. $\endgroup$ – ODP Mar 17 '12 at 10:54
  • $\begingroup$ Some of the prices look astonishing, but you should be able to get a second hand copy reasonably cheaply. I'm sure there other books as good - I just remember it as being easy to learn from when I was a student. The fact it's still in print after so long is also a good sign. $\endgroup$ – John Rennie Mar 17 '12 at 14:50

Your questions are great, the problem is that the answer comprises several math classes and chapter 4 of Hecht's book.

The problem of acquiring a textbook for you is not one we can solve, but I would encourage you to get a copy of 'Optics' by Eugene Hecht (any edition, you should be able to find it cheap) and then teach yourself the mathematics involved. This book presents a brief history of optics, wave mechanics, some electro dynamics, and then starts on the propagation of light. Very well treated.


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