Optical Physics Definitions


Here is a quick reference to definitions and basic laws which are being used in optical physics:

Reflection is a phenomenon of light when light ray bounces off after striking an object.

Laws of Reflection
  • The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.

  • The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal

Refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle. At the boundary between the media, the wave’s phase velocity is altered, usually causing a change in direction. Refraction depends on the media through which the light rays are travelling which is represented by the refractive index, numbers which are constant for given media

Refractive index, also called index of refraction, measure of the bending of a ray of light when passing from one medium into another.

Critical angle is the angle at which light travelling from a medium with higher n to a medium with lower n will be refracted at 90°; i.e. refracted along the interface

Total internal reflection – If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium

Snell’s Law(Law of Refraction): gives us a way of predicting the amount of bend. It involves the angles that the incident ray and the refracted ray make with the normal to the surface at the point of refraction

Aperture: The aperture of a lens is an opening through which light enters. Logically the larger the size of the aperture the more light will enter.

Focal length is defined as the distance from the surface of a lens or mirror to the point where the light rays converge to form an image(the point of focus). Focal length of a convex lens is represented with positive(+) sign while focal length of concave lens is represented with negative(-).

Wavelength is the spatial period of a periodic wave—the distance over which the wave’s shape repeats. It is represented with Greek letter lambda(λ).

Optical frequency is the oscillation frequency of the corresponding electromagnetic wave. 

Angle of Incidence: the angle which an incident line or ray makes with a perpendicular to the surface at the point of incidence

Angle of Reflection: the angle made by a reflected ray with a perpendicular to the reflecting surface.