# Total internal reflection

1. Light traveling in air strikes a glass surface with n = 1.48. For what range of angles will total internal reflection occur?

2. sinΘc = n2/n1

3. I did this equation with air as n2 and glass as n1 and then got Θc=42.5°. After that I subtracted that from the normal (90°) and got 47.5°. Is this the right way to approach this? Just for the record this is for AP Physics B so no calculus should be used. Thank you!

## Answers and Replies

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The question seems to have it backwards. It says " Light traveling in air strikes a glass". Shouldn't it be the other way around?

Why are you subtracting if from 90°?

I did that because from air to glass it makes the sin then not exist. So switched it and because I switched it I then subtracted the 90 degrees.

Switching it changes the question (which may or may not be necessary. May be the original question has a typo. May be not).
Subtracting from 90° makes no sense.

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So what should I do?

collinsmark
Homework Helper
Gold Member
So what should I do?
Go back to the original phrasing of the problem and the original equation,

$$\sin \left( \theta_c \right) = \frac{n_2}{n_1}$$
Now the light starts off in the glass. So what's the original index of refraction, $n_1$ or $n_2$ ?

So what should I do?
Nothing. You're done. If you conclude there was no typo then, as you said, there is no sinθ, and if there is a typo than you already solved it in the OP, except that you shouldn't subtract your answer from 90°. There is no reason to do that.

Ok. Cool then. Thanks a lot

light refracts towards the normal when it travels from a rearer medium to a denser medium so how can we see a perfect image in the mirror it also consits of glass? please answer as fast as possible

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light refracts towards the normal when it travels from a rearer medium to a denser medium so how can we see a perfect image in the mirror it also consits of glass? please answer as fast as possible
What will happen when it again go out to air? (From a high dense to low dense medium?)
Can you answer this question?

The ray will bend away from the medium

But sir there will be a difference as the ray will reflect back from where it is incident.

Ooooooooh. Ok I got it now. Thanks for everything