Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

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

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?

share

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

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

3  
What is up with this flood of basic optics questions? Just get a textbook already –  user2963 Mar 15 '12 at 17:47
5  
And if you understand that equation, the answer should be obvious. –  user2963 Mar 15 '12 at 17:47
    
What haven't you understood? Ditto zephyr on both counts. –  Manishearth Mar 15 '12 at 18:14
    
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 –  Olly Price Mar 15 '12 at 18:25
    

2 Answers 2

up vote 2 down vote accepted

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!

share
    
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. –  Olly Price Mar 15 '12 at 18:33
    
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. –  Olly Price Mar 15 '12 at 18:37
1  
@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. –  user2963 Mar 15 '12 at 19:42
    
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. –  Olly Price Mar 17 '12 at 10:54
    
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. –  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.

share

This site is currently not accepting new answers.

Not the answer you're looking for? Browse other questions tagged .