Question

When light passes from air to glass, its speed .

• A. remains the same
• B. increases
• C. decreases

Answer 1

The correct option is C decreases

The speed of light depends on the optical density (refractive index) of the medium. Light travels faster in a medium of lower refractive index than in one with higher refractive index. As glass is optically denser than air, light travels slower in glass than in air. So, when light passes from air to glass, its speed decreases.