Light Bending at a Glass Surface

A ray of light travels through the air and meets the flat face of a glass block. Part of the light bounces back into the air, and part of it goes into the glass and bends because its speed changes.

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In the picture

The incoming ray in air, travelling towards the glass surface
The dashed normal, perpendicular to the surface at the point where the ray strikes
The angle of incidence, between the incoming ray and the normal
The reflected ray, leaving the surface back into the air
The refracted ray, bent towards the normal inside the glass

Examples

A straw in a glass of water looks broken at the waterline.
A mirror on a wall sends sunlight back across the room.

Key takeaways

Light reflects at the same angle it arrives, measured from the normal.
Light bends when it passes into a material where it travels at a different speed.