The bending of a wave as it passes from one medium to another with a different refractive index is due to a phenomenon called refraction. Refraction occurs because the speed of the wave changes as it enters a medium with a different refractive index.
The refractive index of a medium is a measure of how much the medium can slow down or speed up the propagation of light compared to a vacuum. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. When a wave encounters a change in refractive index at an angle, the change in speed causes the wavefront to change direction, resulting in the bending of the wave.
According to Snell's law, which describes the relationship between the incident angle, the refracted angle, and the refractive indices of the two media, the bending of the wave is governed by the following principles:
Change in Speed: When a wave crosses a boundary between two media with different refractive indices, its speed changes. If the wave enters a medium with a higher refractive index, it slows down, and if it enters a medium with a lower refractive index, it speeds up.
Change in Direction: As the wave encounters the boundary, the change in speed causes a change in direction. The wavefront bends toward or away from the normal, which is an imaginary line perpendicular to the boundary surface. The degree of bending depends on the angle of incidence, the refractive indices of the media, and the wavelength of the wave.
Conservation of Energy and Momentum: The bending of the wave is a result of the conservation of energy and momentum. The wave changes direction to maintain a balance between the energy and momentum of the wavefront.
It's important to note that the refractive index itself is influenced by the physical properties of the medium, such as its density and the behavior of atoms or molecules in the material. These factors affect the interaction between the electromagnetic wave and the medium, leading to variations in the refractive index and subsequent bending of the wave.
The phenomenon of refraction has numerous practical applications, such as the focusing of light by lenses, the formation of rainbows, the operation of optical fibers, and the correction of vision problems using eyeglasses or contact lenses.