Reflection and Refraction

Reflection

Reflection is the bouncing back of a wave when it hits a surface that it cannot pass through. This is what allows mirrors and shiny surfaces to create reflections.
All waves - sound, light, water, etc. - can be reflected. Reflective surfaces are smooth and shiny, such as a mirror or a calm pond. Rough surfaces scatter light in all directions.
When a wave hits a reflective surface, the angle of incidence (the angle between the incoming wave and an imaginary line perpendicular to the surface) is equal to the angle of reflexion (the angle between the reflected wave and the same imaginary line).
A normal line is drawn at a right angle to the boundary surface of two different media at the point of incidence.

Refraction is the change in direction of a wave as it changes its speed, like when moving from one medium into another (e.g., light going from air into water).
It’s important to remember that refraction occurs because waves travel at different speeds in different mediums.
A wave moving into a denser medium (like light going from air into water) slows down and bends towards the normal line. If the wave is going out of a denser medium into a less dense one, it speeds up and moves away from the normal line.
The angle of incidence and the angle of refraction are the angles between the incident and refracted waves and the normal line, respectively. The ratio of their sines is constant for a given pair of media and is known as Snell’s law.
Refraction leads to several optical phenomena, such as the dispersion of light by a prism, the operation of lenses, and the mirage effect.