Assume that a light ray incident on a spherical raindrop at an angle measured with respect to the surface normal undergoes one internal reflection before leaving the raindrop, as shown below.
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Show that if and , then the deflection angle of the light ray is (in radians):
The deflection angle is the angle between the incident ray and the outgoing ray, and is the angle of refraction for the light ray incident from air and entering water. To compute the deflection angle, what quantities must be known?