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SAT® Subject Test in Physics

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Moderate

Critical Angle for Diamond

SATPHY-H3KXG1

The index of refraction for diamond is 2.42. For a diamond in the air ($\text{index of refraction} = 1.00$), what is the smallest angle that a light ray inside the diamond can make with a normal and completely reflect back inside the diamond (the critical angle)?

A

$90^{\circ}$

B

$45^{\circ}$

C

$68^{\circ}$

D

$66^{\circ}$

E

$24^{\circ}$