Question

So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the vacuum between the atoms?

Answer 1

Light slows down when it travels through a medium due to interactions with atoms or molecules. Refraction occurs when light changes direction as it passes from one medium to another.

Step-by-step explanation:

When light travels through a medium such as glass, it slows down because of the interactions between the light waves and the atoms or molecules in the medium. This interaction causes the light waves to get absorbed and re-emitted by the atoms, which takes some time and leads to a slower overall speed of light.

Light can be thought of as traveling in a vacuum between the atoms, but it still interacts with the atoms, leading to a slower speed. The refractive index of a material represents how much it slows down light compared to its speed in a vacuum. The greater the refractive index, the slower light travels through that material.

When light passes from one medium to another, it changes direction because the change in speed causes it to bend. This bending of light is known as refraction. The extent of the bending depends on the refractive indices of the two media and the angle at which the light hits the boundary between them.