Physics Help

[Derosion]

I have completed a lab for Physics (Optics) and I am now doing the given questions.

I am stuck on a few and also a bit confused about them.

Questions:

- The critical angle for diamond is 24 degrees. The critical angle for benzene is 42 degrees. Which of the following angles of incidence would results in total internal reflection in diamond and which in benzene?

A)20 degrees B)25 degrees C)30 degrees D)35 degrees E)40 degrees F) 45 degrees

That's the question, if you know, can you be kind enough to supply how you figured it out? I'm clueless .

The other questions is,

If the critical angle of a substance if 47 degrees, identify the substance. Use table 1, p. 437

Well, I can't show you guys my table. But here's a site where it shows you the table (indexes of refraction)
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/indrf.html

I hate my teacher >_<.

If you guys can help, please post up .

 

[Make it Drizzle]

ok,maybe soon.

 

[DeXoh]

Typed out a long mathematical response and I forgot that any angle above the critical angle would result in total internal refraction. So for diamond thats B C D E and F. For benzene that's F.

For the second problem,

Critical angle = 47 degrees

Take Snell's law. Substitute 90 degrees for the angle of refraction because that's essentially what total internal refraction is.

n1sinx1=n2sin(90)

Sin of 90 degrees is 1, so you're left with

n1sinx1=n2

Solve for index of refraction of the incident medium, and we're going to assume the refracting medium is air.

n1=n2/(sinx1)=(1.00029)/(sin(47))=1.368

That could be ethyl alcohol or acetone according to the web chart, but check the value with your book.

 

[malyce]

DeXoh already covered it but I'd like to make clear: Snell's law is your friend for almost all refraction through a medium.