# Physics Problem: What is the smallest angle θ1 for which a laser beam will undergo total internal reflection...?

What is the smallest angle θ1 for which a laser beam will undergo total internal reflection on the hypotenuse of the glass prism in the figure?

Thanks for the help

### 2 Answers

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- RealProLv 79 months agoFavorite Answer
Assuming 1.5 for index of refraction of glass, and inxident beam travels in air.

The hypotenuse will undergo complete internal reflection if it enters at an angle of incidence to the hypotenuse of more than arcsin(1/1.5) = 41.81°

So under the given configuration it has to travel through the prism at minimally 11.81° to the horizontal.

Minimum incident angle arcsin(1.5 * sin11.81°) = 17.88° round appropriately

Try for the index of refraction you were given for glass.

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The problem didn't specify the index of refraction, but it seems it was 1.5, 17.88 is right! Thank you very much