Why is angle of refraction smaller than angle of incidence?

Question

Working on investigations into Snell's law when the general thought occurred to me .... when passing from air to perspex we know the refracted light ray has a smaller angle (measured from the vertical) than the incidence ray .... but why?

Anyone know?

Answer 1

It's all because the light slows down in perspex (or glass, water etc). So the wavefronts don't travel so far` per second and appear to bend - the derivation of Snell's law comes just from this

Answer 2

Because of nanoscopic imperfections in the perspex that will deflect the path of the light; also a tiny amount of the light will get converted to heat energy on passage through the perspex, causing it to flex.