Reflection, Refraction, and Diffraction

Waves can and do meet boundaries in their medium. When a wave meets a boundary, it can be reflected or transmitted. Reflection can be partial or complete. Reflection can also involve a phase flip (change of phase of 180 degrees.) Transmitted waves are refracted or diffracted: Refraction occurs when a wave crosses a boundary from one medium to another. A wave entering a medium at an angle will change direction. Diffraction refers to the "bending of waves around an edge" of an object. Diffraction depends on the size of the object relative to the wavelength of the wave. All these phenomena apply to electromagnetic waves, such as light waves, as well as to pressure waves and water waves.