What is the difference between reflection, refraction, and diffraction?
Reflection of light occurs when light rays strike a surface and bounce back or reflect off it. In this case, the Law of Reflection is valid, ie the angle of incidence equals the angle of reflection.
Refraction is when light rays enter a different medium of different optical density and change direction or bend. In this case, Snell's Law is valid to calculate the degree of refraction. If it enters a more optical dense medium it is refracted towards the normal.
Diffraction is when light waves bend around obstacles placed in their path and bend into the shadow region. This phenomenon is responsible for interference patterns being formed on screen placed behind diffraction apparatus for example. Equations are valid for calculating conditions and positions of interference bands.