## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

$n_1 \lt n_2$
We can write Snell's Law: $n_1~sin~\theta_1 = n_2~sin~\theta_2$ where $n_i$ is the refractive index and $\theta_i$ is the angle as measured from the perpendicular with the surface boundary. If $\theta_i$ is larger, then $n_i$ must be smaller in order for the equality to hold. Since $\theta_1 \gt \theta_2$, then $~~n_1 \lt n_2$