Light waves travel in straight paths, known as rays, in homogeneous and isotropic mediums. When light passes through a uniform medium, such as air or a vacuum, it propagates in a straight line. This is known as rectilinear propagation.
However, when light encounters a change in medium, such as passing from air to water or from air to a glass prism, it can undergo various phenomena such as refraction, reflection, and diffraction. These phenomena can alter the path of light waves. Here are some common paths that light waves can follow:
Reflection: When light waves encounter a smooth surface, such as a mirror, they bounce off the surface in a process called reflection. The angle of incidence (the angle between the incident ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal to the surface).
Refraction: Refraction occurs when light waves pass from one medium to another, causing them to change direction. The change in direction is due to a change in the speed of light as it enters a different medium. The bending of light at the interface between two media is governed by Snell's law, which relates the angles of incidence and refraction to the refractive indices of the two media.
Diffraction: Diffraction refers to the bending or spreading of light waves around obstacles or through narrow openings. It occurs when the size of the obstacle or the opening is comparable to or smaller than the wavelength of light. Diffraction can cause light waves to spread out and produce interference patterns.
Scattering: Scattering is the random redirection of light waves by particles or irregularities in a medium. It causes light to be redirected in various directions. Examples of scattering include Rayleigh scattering, which gives the sky its blue color, and Mie scattering, which occurs when light interacts with larger particles or droplets.
Interference: Interference occurs when two or more light waves overlap and combine. Depending on the phase relationship between the waves, constructive interference can occur, resulting in brighter regions, or destructive interference can occur, resulting in darker or canceled regions.
The actual path that light waves take can depend on the specific conditions, including the properties of the medium, the nature of the surfaces or obstacles encountered, and the interaction with other waves.