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

A photon/wave of light doesn’t require an energy source once it’s created. It exists as pure energy and it is its own energy source so it will always go back to its expected speed after it passes through some medium that “slows” its progress.