How does light accelerate back to its original speed after refraction from another medium e.g. glass or water

Question

The speed of light slows as it traverses through a different medium, but after slowing it finds a way to accelerate back to original speed as it exits that medium. How does it do that?

In: 93

Answer 1

The speed of light does not actually change at all, it only appears to. A common misconception is that photons are absorbed and re-emitted, but this is wrong. The real explanation is quite hard to ELI5, but I’ll give it a go.

It starts by understanding that light behaves a bit like ripples in a pool. As these ripples pass through stuff, the stuff jiggles a bit. But the jiggling stuff causes it’s own, slightly delayed ripples. When you add these ripples to the original ripples it looks like one ripple moving slower. So we say “light moves slower” even though the original ripples and the delayed ripples travel at full speed.