# Homework Help: Optics question - Don't know if anyone can help

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1. Aug 30, 2014

### randybryan

I've attached a screenshot of the question, and I have to admit I'm really struggling. I don't know if anyone will be able to help as optics is very diagram-dependent, but perhaps you can give me a hint without needing to draw anything.

I'm stuck on (ii) a)

The first thing I did was use Snell's law to give sin(α)=n sin(β), and that's about as far as I've got in progress. I realise I need to get sin(β) in terms of θ, but nothing I seem to do can get me the answer. Do I need to consider the angle γ as well? I know that n sinγ≈ 1, but I'm just adding another variable to the problem!

(I have an exam soon, hence the sudden influx of questions)

#### Attached Files:

• ###### Screen Shot 2014-08-30 at 16.42.49.png
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2. Aug 30, 2014

### TSny

Hello.

See if you can use just geometry to relate the angles β, γ, and θ.

Hint: It might be helpful to draw an auxiliary vertical line through the point where the ray strikes the wall of the cone.

3. Aug 30, 2014

### randybryan

Of course!! I put the line in every other place but there. Thanks for the help