# Prism refracting problem help please.

1. Feb 14, 2005

### Twigs

A prism shown i has a refractive index of n, and the angles A are theta. Two light rays m and n are parallel as they enter the prism.

What is the angle between them after they emerge?(In radians)

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2. Feb 14, 2005

### dextercioby

What did you do/try to do...?

Daniel.

3. Feb 14, 2005

### Twigs

I assume you use n_1*sin(theta)=n_2*sin(theta_2).

And since its 90 degrees, it would just be equal to 1, so I get 1=n_2*sin(theta_2) but im afraid that im assuming too much. Then you do it again for the light going out of the prism.

4. Feb 14, 2005

### dextercioby

Because of the normal incidence,the rays enter the prism nondeviated...You must apply Snell'-Descartes law for the outgoing...

Daniel.

5. Feb 14, 2005

### Twigs

6. Feb 14, 2005

### Twigs

no, thats answer is wrong, any help?

7. Feb 14, 2005

### dextercioby

I'm really sorry,i cannot give you any more details,because it's basically a geometry problem.The incident angle is "\theta" for both rays...Compute the reflection angle,which is indeed "\arcsin (n\sin\theta)" and then use the symmetry of the problem and basic geometry knowledge to solve it...

Daniel.

8. Feb 14, 2005

### Twigs

2*arcsin(n*sin(theta))+pi/2
I'm getting $angle=2[\arcsin (n\sin\theta)-\theta]$