If the light leaves a glass block (n = 1.5) with an angle of refraction of 70°. what is the angle of incidence?

The angle of incidence is 38.8°.

Explanation:

let n1 = 1.5 be the refractive index of glass and ∅1 be the angle of incidence, let n2 be the refractive index of air and ∅2 be the angle of refraction.

by Snell's law:

n1*sin (∅1) = n2*sin (∅2)

sin (∅1) = n2*sin (∅2) / n1

= (1) * sin (70) / 1.5

∅1 = 38.8°

Therefore, the angle of incidence is 38.8°.