Question

why the speed of light changes in different medium? if it is due to the atoms or matter being as a medium then why is optical density different than mass density?​

Answer 1

Answer:

Light moves slower through denser media because more particles get in its way. Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.

Answer 2

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Waves. Refraction is an effect that occurs when a light wave, incident at an angle away from the normal, passes a boundary from one medium into another in which there is a change in velocity of the light. Light is refracted when it crosses the interface from air into glass in which it moves more slowly.