When light strikes a lens, it is propagating in air as the first medium and glass as the second medium. Air has an index of refraction of 1 and glass might have an index of refraction of 1.5, depending on the type of glass. If the light strikes the lens at an angle of 30 degrees from the normal, we can use Snell's law to find the refracted angle, theta2. Doing the algebra:
sin(theta2) = sin(theta1)/n2 = sin(30)/1.5 = 0.33
theta2 = 19 degrees.
When the light passes from air to glass, it is refracted to a smaller angle from the normal. When the light leaves the lens it passes from glass to air and is refracted to a larger angle.
Read more at Suite101: Refraction of Light: Refractive Index, Snell's Law in Optics, & Refracting Light in Media | Suite101.com http://paul-a-heckert.suite101.com/refra…
http://paul-a-heckert.suite101.com/refra…