Light bends: refraction · Pulse Beat
Light travels more slowly in water or glass than in air, so it bends when it crosses from one to the other at an angle. This is refraction.
Light travels more slowly in water or glass than in air, so it bends when it crosses from one to the other at an angle. This is refraction.
Snell's law gives the angle: n₁ sin θ₁ = n₂ sin θ₂. Here n is a material's refractive index (about 1.00 for air, 1.33 for water, 1.5 for glass) and θ is the angle from the line perpendicular to the surface.
That is why a straw in a glass of water looks bent, and why a swimming pool looks shallower than it is.
A rainbow is refraction plus reflection. Sunlight enters a raindrop, reflects off the back, and leaves, bending by a slightly different amount for each colour. You see red at the top of the arc and violet at the bottom.