Concept
Imagine you’re driving your car down the road on a
summer day. You stop paying attention for a few moments, and
drive your car into giant wall of orange jello. The jello
wall isn’t perpendicular to the road, though, so picture in
your head how one corner of your car hits the wall slightly
before the rest of it. That side of your bumper that hits
the wall first will now be facing more resistance than other
side. The striking side slows down slightly, while the other
side continues at the same speed. This causes the car to
pivot slightly toward a perpendicular angle to the jello
wall. In a moment, your entire car will be in the wall of
jello, but it will be moving at a slightly different angle.
Now imagine that you
finally make it out of jello covered area. The corner of
your that originally entered the wall first now exits
the wall first. This decreases resistance on that side
of the car first, causing it to speed up. The car
consequently turns away from that side, restoring the
car to the initial angle it was traveling.
This is basically how
Snell’s Law works. When light is travelling at an angle
into a denser medium, it bends, or refracts, towards the
angle perpendicular to the surface of the medium, also
known as the normal angle. And when light travels from a
dense medium to a less dense medium, light refracts away
from the normal angle.