Prism (optics)
From Freepedia
Image:PrismAndLight.jpg In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colours (colours of the rainbow). The traditional geometrical shape is that of a triangular prism, with a triangular base and rectangular sides. Some types of optical prisms are not in fact in the shape of geometric prisms.
As light moves from one medium (e.g. air) to another denser medium (the glass of the prism), it is slowed down and as a result either bent (refracted) or reflected. The angle that the beam of light makes with the interface as well as the refractive indices of the two media determine whether it is reflected or refracted, and by how much (see refraction, total internal reflection).
Reflective prisms are used to reflect light, for instance in binoculars, since they are easier to manufacture than mirrors. Dispersive prisms are used to break up light into its constituent spectral colours because the refractive index depends on frequency (see dispersion); the white light entering the prism is a mixture of different frequencies, each of which gets bent slightly differently. Blue light is slowed down more than red light and will therefore be bent more than red light. There are also polarizing prisms (also known as birefringent prisms) which can split a beam of light into components of varying polarization.
Isaac Newton first thought that prisms split colours out of colourless light. Newton placed a second prism such that a separated colour would pass through it and found the colour unchanged. He concluded that prisms separate colours. He also used a lens and a second prism to recompose the rainbow into white light.
Types of prisms
Reflective prisms:
- Pentaprism
- Porro prism
- Porro-Abbe prism
- Abbe-Koenig prism
- dove prism
- dichroic prism
- Amici roof prism
Dispersive prisms:
Polarizing prisms:
See also
