# Homework Help: Help on optics problems please they are due tonight

1. Jul 15, 2004

### supermenscher

help on optics problems...please...they are due tonight!!!

Two mirrors meet at an 125 degree angle. If light rays strike one mirror at 125 degrees, what angle do they leave the second mirror? I got 5 degrees and I tried negative 5 degrees, but both of those answers are wrong.

A diver shines a flashlight upward from beneath the water at a 47.5 degree angle to the vertical. At what angle does the light leaver the water. I got 71.5 degrees, and that answer was incorrect.

LIght is incident on an equlateral crown glass prism at a 42 degree angle to the normal on one face. Calculate the angle at which light emerges from the oppoiste face. Assume n = 1.56. I tried this problem twice, and got two wrong answers.

2. Jul 15, 2004

### Staff: Mentor

In order to get the help you need, you must show your work so we can see what you are doing wrong.
I assume you are talking about plane mirrors? If so, I understand what "meeting at 125 degrees" probably means. But what does light striking at 125 degrees mean? Usually the angle is given with respect to the normal, thus can only go as high as 90 degrees.

Apply Snell's law of refraction. You mixed up the indices of refraction for air and water.

Apply Snell's law of refraction and some triangle geometry.

3. Jul 15, 2004

### supermenscher

Sorry I made a typo, the light ray strikes one mirror at 40 degrees

4. Jul 15, 2004

### supermenscher

Thanks for your help doc al

5. Jul 15, 2004

### Staff: Mentor

All three solved correctly?

6. Jul 15, 2004

### supermenscher

Yes, I followed the formulas given and plugged in the numbers

7. Jul 15, 2004

### supermenscher

I got the other 2 right, but I still can't get the first one with the mirrors and angle. Thank you for you help so far

8. Jul 16, 2004

### Staff: Mentor

It's probably too late for your deadline, but the first one is just the law of reflection ($\theta_i = \theta_r$) with a little triangle geometry thrown in.

9. Jul 16, 2004

### supermenscher

thank u doc al