The angle of refraction measures the angle to which light bends as it passes across the boundary between different media.
- The angle of refraction is measured between a ray of light and an imaginary line called the normal.
- In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
- See this diagram for an explanation: Refraction of a ray of light
- If the boundary between the media is curved, the normal is drawn perpendicular to the boundary.