When a light ray passes from air into glass, what happens to its speed? Draw a diagram to show which way the ray of light bends.

When a ray of light passes from air (rarer medium) into glass (denser medium), its speed decreases and it bends towards the normal. 

 

Explanation

The angle of refraction or the amount of bending of light depends on the refractive index  of the two media.

1. When light passes through a low refractive index, like air (faster medium or optically rarer medium) to a high refractive index, like glass(slower medium or optically denser medium), its speed decreases and bends towards the normal. 

2. When light passes through a high refractive index, like glass (slower medium or optically denser medium) to a low refractive index, like air (faster medium or optically rarer medium) its speed increases and bends away from the normal.