Classical optics is divided into two main branches: geometrical
optics and physical optics. In geometrical, or ray optics, light is
considered to travel in straight lines, and in physical, or wave optics,
light is considered to be an electromagnetic wave.
Geometrical optics can be viewed as an approximation of physical optics which can be applied when the wavelength of the light used is much smaller than the size of the optical elements or system being modelled.
Geometry of reflection and refraction of light rays
Geometrical optics, or ray optics, describes the propagation
of light in terms of "rays" which travel in straight lines, and whose
paths are governed by the laws of reflection and refraction at
interfaces between different media.
When a ray of light hits the boundary between two transparent materials, it is divided into a reflected and a refracted ray.
The laws of reflection and refraction can be derived from Fermat's principle which states that the path taken between two points by a ray of light is the path that can be traversed in the least time.
Geometrical optics can be viewed as an approximation of physical optics which can be applied when the wavelength of the light used is much smaller than the size of the optical elements or system being modelled.
Geometrical optics
Main article: Geometrical optics
When a ray of light hits the boundary between two transparent materials, it is divided into a reflected and a refracted ray.
- The law of reflection says that the reflected ray lies in the plane of incidence, and the angle of reflection equals the angle of incidence.
- The law of refraction says that the refracted ray lies in the plane of incidence, and the sine of the angle of refraction divided by the sine of the angle of incidence is a constant.
The laws of reflection and refraction can be derived from Fermat's principle which states that the path taken between two points by a ray of light is the path that can be traversed in the least time.
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