The Speed of Light in a Material Is $0.41 \mathrm { c }$

Multiple Choice

The speed of light in a material is $0.41 \mathrm { c }$ . What is the critical angle of a light ray at the interface between the material and a vacuum?

A) $22 ^ { \circ }$
B) $24 ^ { \circ }$
C) $17 ^ { \circ }$
D) $19 ^ { \circ }$