Reflection and Refraction

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GRE Subject Test: Physics › Reflection and Refraction

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1

A beam of light travels through a medium with index of refraction until it reaches an interface with another material, with index of refraction . No light is transmitted into the second material. At what angle (measured from the plane of the interface between the two materials) does the beam hit the second material?

$60^\circ$

$30^\circ$

$90^\circ$

$45^\circ$

This situation is impossible.

Explanation

Total internal reflection occurs at the angle:

$\theta=\sin^{-1}(\frac{n_2}{n_1})=\sin^{-1}(\frac{1.2}{2.4})=\sin^{-1}(\frac{1}{2})=30^o$

However, this angle is measured from a line normal to the plane of the interface; the angle we want, therefore, is , which is $60^\circ$ .

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