# What is the equation for Snell's law?

Apr 14, 2014

where
${n}_{1}$ is the index of refraction of the first substance that light travels through
${\theta}_{1}$ is the angle of incidence
${n}_{2}$ is the index of refraction of the second substance that light travels through
${\theta}_{2}$ is the angle of refraction

Then you need to isolate your unknown.

Example:

Light in air (${n}_{1}$ = 1.0003) is incident upon a block of crown glass (${n}_{2}$ = 1.52) at an angle of ${35.0}^{o}$. What is the angle of refraction?

${n}_{1}$ sin ${\theta}_{1}$ = ${n}_{2}$ sin ${\theta}_{2}$
(Isolate sin ${\theta}_{2}$ by dividing both sides by ${n}_{2}$)
${n}_{1}$ sin ${\theta}_{1}$ / ${n}_{2}$ = sin ${\theta}_{2}$
(1.0003) (sin 35.0) / 1.52 = sin ${\theta}_{2}$
0.5737 / 1.52 = sin ${\theta}_{2}$
0.3775 = sin ${\theta}_{2}$
(To find ${\theta}_{2}$, you need to find the inverse sine of this value. On your calculator, press the 2nd function key, then the sine key.)
${22.2}^{o}$ = ${\theta}_{2}$