# physics optics question

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• May 4th 2008, 07:57 AM
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physics optics question
An equilateral triangular glass prism has an index of refraction of 1.52. Calculate the angle of incidence at which a ray of light would traverse the prism symmetrically (the angle of emergence equal to the angle of incidence).

please help..thankss
• May 4th 2008, 09:26 AM
TwistedOne151
Re: Refraction
If you draw a diagram of the triangle, you see that one has symmetry only if the segment of the ray's path within the prism is parallel to one side of the prism (the side through which it doesn't pass), leading to an angle of refraction of 30°. Thus, we use Snell's law (with the refractive index of air being approximated as 1):
$n_1\sin\theta_1=n_2\sin\theta_2$
$1\cdot\sin\theta_1=1.52\sin{30^{\circ}}$
$\sin\theta_1=1.52\cdot\frac{1}{2}$
$\sin\theta_1=0.76$
Your calculator should give you the answer to that.

--Kevin C.