# Damn light & lens problems

1. May 5, 2007

### jst

Damn light & lens problems :(

The problems come from a homework that I've already submitted. I got some right and some wrong, but the ones that I did correctly I'm not too confident in method (which including guessing at times). There's really not really a lot of calculations involved in solving these, but it seems to me I'm just not fully understanding a couple of key concepts. Since some of these problems are similar, I'm not asking for them to be worked out...maybe just some pointers? Any help is appreciated.

Thanks,

Jason

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Last edited by a moderator: Apr 22, 2017 at 5:22 PM
2. May 5, 2007

### jst

Great!!! This forum is full of lifesavers :D

3. May 5, 2007

### dontdisturbmycircles

Ok what are you having troubles with? Do you want a general problem solving strategy for mirrors and lenses or do you have specific questions?

4. May 5, 2007

### jst

I think a "general problem solving strategy" would do it....a lot of these problems seem similar. If you understand these problems, anything you think that would be helpful would be really cool.

Last edited: May 5, 2007
5. May 5, 2007

### dontdisturbmycircles

Ok well for the first one, and any other refraction question you must use Snells law:

$$n_{i}*sin(\theta_{i})=n_{r}*sin(\theta_{r})$$

where $$n_{i}$$ is the index of refraction for the medium from which the light ray is originating (in the case of the first question, 2.42). The angles are always measured with respect to the normal line (a line drawn perpendicular to the surface) The index of refraction for air is 1.00. Notice how the question is asking what is the minimum angle, which means that the light ray would refract with an angle of refraction equal to 90degrees (it would not exit the diamond). This is called total internal reflection.

So you would basically just plug in ni=2.42 nr=1.00 and $$\theta_{r}=90deg$$ and solve for the angle of incidence...

This is a lot of stuff to explain lol. Its like a whole chapter out of a textbook. (I would enjoy helping you) Just start asking specific questions and I will try my best to answer them.

Do you know how to use the mirror equation?

$$\frac{1}{f}=\frac{1}{d_{i}} + \frac{1}{d_{o}}$$

Does this make any sense?

Last edited: May 5, 2007
6. May 5, 2007

### jst

I think I've used that equation...is that for #3?