The figure shows a point source of unpolarized light at A inside a uniform transparent crystal. The ray AO in the crystal strikes the plane surface SS' making an angle of 30° with the normal. This angle is the critical angle for transmission into air.

-If point A is 16 cm below the plane SS',what is the radius of the largest circle at the air-crystal interface through which light can emerge from the crystal?
A)9.2 cm
B)16.0 cm
C)18.4 cm
D)27.0 cm
E)32.0 cm

Question

The figure shows a point source of unpolarized light at A inside a uniform transparent crystal.  The ray AO in the crystal strikes the plane surface SS' making an angle of 30° with the normal.   This angle is the critical angle for transmission into air.

-If point A is 16 cm below the plane SS',what is the radius of the largest circle at the air-crystal interface through which light can emerge from the crystal?
A)9.2 cm 
B)16.0 cm 
C)18.4 cm 
D)27.0 cm 
E)32.0 cm

Quizplus · Accepted Answer

The radius of the largest circle is determined by the critical angle for total internal reflection. Using Snell's Law and the geometry of the situation, the radius is calculated to be 9.2 cm.

The Figure Shows a Point Source of Unpolarized Light at a Inside