# prism (optics)

If a shaft of light entering a prism is sufficiently narrow, a spectrum results.
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use "prism" usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms are typically made out of glass, but can be made from any material that is transparent to the wavelengths for which they are designed.

A prism can be used to break light up into its constituent spectral colors (the colors of the rainbow). They can also be used to reflect light, or to split light into components with different polarizations.

## How prisms work

Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). This speed-change causes light striking the boundary between two media at an angle to be refracted and enter the new medium at a different angle (Huyghens principle), or to be reflected away from it. The amount of reflected light and the degree of bending of the light's path will depend on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media (Snell's law). The refractive index of a medium varies with the wavelength or color of the light used, a phenomenon known as dispersion, and this causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow. This effect can be used to separate a beam of white light into its constituent spectrum of colors.

In Isaac Newton's time, some believed that prisms created new colors. Newton passed individual colors from one prism's spectrum through a second prism and found the color unchanged, and concluded from this that that these different colors must have already been present in the original light — the prism did not create new colors, but merely separated the colors that were already there. He also used a lens and a second prism to recompose the rainbow back into white light. This experiment has become a classic example of the methodology introduced during the scientific revolution. The results of this experiment dramatically transformed the field of metaphysics, leading to John Locke's primary vs secondary quality distinction.

Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, total internal reflection occurs and all of the light is reflected. This makes a prism a useful substitute for a mirror in some situations.

## Types of prisms

Animated image: A triangular prism, dispersing light

### Dispersive prisms

Dispersive prisms are used to break up light into its constituent spectral colors because the refractive index depends on frequency; 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.

### Reflective prisms

Reflective prisms are used to reflect light, for instance in binoculars.

### Polarizing prisms

There are also polarizing prisms which can split a beam of light into components of varying polarization. These are typically made of a birefringent crystalline material.

## References

• Hecht, Eugene (2001). Optics (4th ed.). Pearson Education. ISBN 0-8053-8566-5.

Optics (ὀπτική appearance or look in Ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter.
Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for
Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
In geometry, a triangular prism or three-sided prism is a type of prism; it is a polyhedron made of a triangular base, a translated copy, and 3 faces joining corresponding sides.
prism is a polyhedron made of an n-sided polygonal base, a translated copy, and n faces joining corresponding sides. Thus these joining faces are parallelograms. All cross-sections parallel to the base faces are the same. A prism is a subclass of the prismatoids.
Glass is a noncrystalline material that can maintain indefinitely, if left undisturbed, its overall form and amorphous microstructure at a temperature below its glass transition temperature.
In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves.
spectrum (plural spectra) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a
Color or colour[1] (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, yellow, blue, black, etc.
Rainbows are optical and meteorological phenomena that cause a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere.
Reflection is the change in direction of a wave front at an between two dissimilar media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.
polarization (Brit., polarisation) is the property of electromagnetic waves, such as light, that describes the direction of the transverse electric field. More generally, the polarization of a transverse wave describes the direction of oscillation in the plane
Speed is the rate of motion, or equivalently the rate of change in position, many times expressed as distance d traveled per unit of time t.

Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as
Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for
Reflection or reflexion may refer to:
• Reflection (physics), a wave phenomenon commonly observed in mirrors.
• Reflection (electrical), reflected voltage in an electrical signal due to an impedance change

An incident is a series of events that involves an attack or series of attacks (compromise and/or breach of security) at one or more sites.

For the usages in mathematics, see:
• incidence (geometry)
• graph (mathematics)

The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. For example, typical glass has a refractive index of 1.
Snell's law (also known as Descartes' law or the law of refraction), is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different isotropic
In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves.
dispersion is the phenomenon that the phase velocity of a wave depends on its frequency.[1] In a prism, dispersion causes the spatial separation of a white light into spectral components of different wavelengths.
Rainbows are optical and meteorological phenomena that cause a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere.
spectrum (plural spectra) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a
Sir Isaac Newton

Isaac Newton at 46 in
Godfrey Kneller's 1689 portrait
Born 4 January 1643 [OS: 25 December 1642]
Scientific Revolution can be dated roughly as having begun in 1543, the year in which Nicolaus Copernicus published his De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) and Andreas Vesalius published his De humani corporis fabrica
Metaphysics is the branch of philosophy that investigates principles of reality transcending those of any particular science, traditionally including cosmology and ontology. It is also concerned with explaining the ultimate nature of being and the world.