# Homework Help: Total internal reflection

1. Apr 16, 2014

### nst.john

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!

2. Apr 16, 2014

### dauto

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°?

3. Apr 17, 2014

### nst.john

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.

4. Apr 17, 2014

### dauto

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.

Last edited: Apr 17, 2014
5. Apr 17, 2014

### nst.john

So what should I do?

6. Apr 17, 2014

### collinsmark

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 $n_2$ ?

7. Apr 18, 2014

### dauto

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.

8. Apr 18, 2014

### nst.john

Ok. Cool then. Thanks a lot

9. Apr 21, 2014

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

10. Apr 21, 2014

What will happen when it again go out to air? (From a high dense to low dense medium?)

11. Apr 21, 2014

### nst.john

The ray will bend away from the medium

12. Apr 21, 2014