Learning Goal:

To practice Tactics Box $18\mathrm{.}1$ Analyzing refraction.

If a ray refracts between $$medium $1$ and medium $2,$ having indices of refraction n$1$ and n$2,$ the ray angles $1$ and $2$ in the two media are related by Snell's law,

n$1$sin$1=$n$2$sin$2.$

This law becomes a central idea in a procedure for analyzing refraction problems, as explained in the following Tactics Box.