A report on Light and Refractive index

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
A ray of light being refracted in a plastic block
The electromagnetic spectrum, with the visible portion highlighted
Refraction of a light ray
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Thomas Young coined the term index of refraction.
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
Diamonds have a very high refractive index of 2.417.
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
A split-ring resonator array arranged to produce a negative index of refraction for microwaves
Hong Kong illuminated by colourful artificial lighting.
In optical mineralogy, thin sections are used to study rocks. The method is based on the distinct refractive indices of different minerals.
Pierre Gassendi.
Light of different colors has slightly different refractive indices in water and therefore shows up at different positions in the rainbow.
Christiaan Huygens.
In a prism, dispersion causes different colors to refract at different angles, splitting white light into a rainbow of colors.
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.
The variation of refractive index with wavelength for various glasses. The shaded zone indicates the range of visible light.
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The colors of a soap bubble are determined by the optical path length through the thin soap film in a phenomenon called thin-film interference.
Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.
Total internal reflection can be seen at the air-water boundary.
The power of a magnifying glass is determined by the shape and refractive index of the lens.
The relation between the refractive index and the density of silicate and borosilicate glasses
A calcite crystal laid upon a paper with some letters showing double refraction
Birefringent materials can give rise to colors when placed between crossed polarizers. This is the basis for photoelasticity.
A gradient-index lens with a parabolic variation of refractive index (n) with radial distance (x). The lens focuses light in the same way as a conventional lens.
The principle of many refractometers
A handheld refractometer used to measure the sugar content of fruits
A differential interference contrast microscopy image of yeast cells

In optics, the refractive index ( refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.

- Refractive index

where θ1 is the angle between the ray and the surface normal in the first medium, θ2 is the angle between the ray and the surface normal in the second medium and n1 and n2 are the indices of refraction, n = 1 in a vacuum and n > 1 in a transparent substance.

- Light
A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

10 related topics with Alpha

Overall

A ray of light being refracted in a plastic block.

Refraction

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Redirection of a wave as it passes from one medium to another.

Redirection of a wave as it passes from one medium to another.

A ray of light being refracted in a plastic block.
Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.
A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.
When a wave moves into a slower medium the wavefronts get compressed. For the wavefronts to stay connected at the boundary the wave must change direction.
A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.
An image of the Golden Gate Bridge is refracted and bent by many differing three-dimensional drops of water.
The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.
Heat haze in the engine exhaust above a diesel locomotive.
Mirage over a hot road.
Water waves are almost parallel to the beach when they hit it because they gradually refract towards land as the water gets shallower.

Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.

For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the refractive indices (n2 / n1) of the two media.

The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.

Wavelength

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Spatial period of a periodic wave—the distance over which the wave's shape repeats.

Spatial period of a periodic wave—the distance over which the wave's shape repeats.

The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.
Sinusoidal standing waves in a box that constrains the end points to be nodes will have an integer number of half wavelengths fitting in the box.
A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue)
Wavelength is decreased in a medium with slower propagation.
Refraction: upon entering a medium where its speed is lower, the wave changes direction.
Separation of colors by a prism (click for animation)
Various local wavelengths on a crest-to-crest basis in an ocean wave approaching shore
A sinusoidal wave travelling in a nonuniform medium, with loss
A wave on a line of atoms can be interpreted according to a variety of wavelengths.
Near-periodic waves over shallow water
Wavelength of a periodic but non-sinusoidal waveform.
A propagating wave packet
Pattern of light intensity on a screen for light passing through two slits. The labels on the right refer to the difference of the path lengths from the two slits, which are idealized here as point sources.
Diffraction pattern of a double slit has a single-slit envelope.
Relationship between wavelength, angular wavelength, and other wave properties.

Examples of waves are sound waves, light, water waves and periodic electrical signals in a conductor.

For electromagnetic waves the speed in a medium is governed by its refractive index according to

The Lorentz factor γ as a function of velocity. It starts at1 and approaches infinity as v approaches c.

Speed of light

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Universal physical constant that is important in many areas of physics.

Universal physical constant that is important in many areas of physics.

The Lorentz factor γ as a function of velocity. It starts at1 and approaches infinity as v approaches c.
Event A precedes B in the red frame, is simultaneous with B in the green frame, and follows B in the blue frame.
The blue dot moves at the speed of the ripples, the phase velocity; the green dot moves with the speed of the envelope, the group velocity; and the red dot moves with the speed of the foremost part of the pulse, the front velocity.
A beam of light is depicted travelling between the Earth and the Moon in the time it takes a light pulse to move between them: 1.255 seconds at their mean orbital (surface-to-surface) distance. The relative sizes and separation of the Earth–Moon system are shown to scale.
Measurement of the speed of light using the eclipse of Io by Jupiter
Aberration of light: light from a distant source appears to be from a different location for a moving telescope due to the finite speed of light.
One of the last and most accurate time of flight measurements, Michelson, Pease and Pearson's 1930–35 experiment used a rotating mirror and a one-mile (1.6 km) long vacuum chamber which the light beam traversed 10 times. It achieved accuracy of ±11 km/s.
Diagram of the Fizeau apparatus
Electromagnetic standing waves in a cavity
An interferometric determination of length. Left: constructive interference; Right: destructive interference.
Rømer's observations of the occultations of Io from Earth
Hendrik Lorentz (right) with Albert Einstein

All forms of electromagnetic radiation, including visible light, travel at the speed of light.

The speed at which light propagates through transparent materials, such as glass or air, is less than c; similarly, the speed of electromagnetic waves in wire cables is slower than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (

Circular polarization on rubber thread, converted to linear polarization

Polarization (waves)

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Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Circular polarization on rubber thread, converted to linear polarization
cross linear polarized
A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).
Electric field oscillation
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Animation showing four different polarization states and three orthogonal projections.
A circularly polarized wave as a sum of two linearly polarized components 90° out of phase
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Color pattern of a plastic box showing stress-induced birefringence when placed in between two crossed polarizers.
Paths taken by vectors in the Poincaré sphere under birefringence. The propagation modes (rotation axes) are shown with red, blue, and yellow lines, the initial vectors by thick black lines, and the paths they take by colored ellipses (which represent circles in three dimensions).
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s-polarized light at each surface, leaving (after many such plates) a mainly p-polarized beam.
Stress in plastic glasses
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the horizontally oriented polarizer preferentially transmits those reflections; rotating the polarizer by 90° (right) as one would view using polarized sunglasses blocks almost all specularly reflected sunlight.
One can test whether sunglasses are polarized by looking through two pairs, with one perpendicular to the other. If both are polarized, all light will be blocked.
The effects of a polarizing filter (right image) on the sky in a photograph
Colored fringes in the Embassy Gardens Sky Pool when viewed through a polarizer, due to stress-induced birefringence in the skylight
Circular polarization through an airplane plastic window, 1989

Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids.

Even in isotropic media, so-called inhomogeneous waves can be launched into a medium whose refractive index has a significant imaginary part (or "extinction coefficient") such as metals; these fields are also not strictly transverse.

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Optics

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The Nimrud lens
Alhazen (Ibn al-Haytham), "the father of Optics"
Reproduction of a page of Ibn Sahl's manuscript showing his knowledge of the law of refraction.
The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)
Cover of the first edition of Newton's Opticks (1704)
Geometry of reflection and refraction of light rays
Diagram of specular reflection
Illustration of Snell's Law for the case n1 < n2, such as air/water interface
A ray tracing diagram for a converging lens.
Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.
When oil or fuel is spilled, colourful patterns are formed by thin-film interference.
Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.
Dispersion: two sinusoids propagating at different speeds make a moving interference pattern. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this case, the phase velocity is twice the group velocity. The red dot overtakes two green dots, when moving from the left to the right of the figure. In effect, the individual waves (which travel with the phase velocity) escape from the wave packet (which travels with the group velocity).
Linear polarization diagram
Circular polarization diagram
Elliptical polarization diagram
A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.
The effects of a polarising filter on the sky in a photograph. Left picture is taken without polariser. For the right picture, filter was adjusted to eliminate certain polarizations of the scattered blue light from the sky.
Experiments such as this one with high-power lasers are part of the modern optics research.
VLT's laser guide star
Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina
The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.
Illustrations of various optical instruments from the 1728 Cyclopaedia
Photograph taken with aperture 32
Photograph taken with aperture 5
A colourful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

is the refractive index of the second material.

A modern pair of glasses

Glasses

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Glasses, also known as eyeglasses or spectacles, are vision eyewear, with lenses (clear or tinted) mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms (known as temples or temple pieces) that rest over the ears.

Glasses, also known as eyeglasses or spectacles, are vision eyewear, with lenses (clear or tinted) mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms (known as temples or temple pieces) that rest over the ears.

A modern pair of glasses
A skyline seen through a corrective lens, showing the effect of refraction
Safety glasses with side shields
Woman wearing sunglasses
Doubleframe eyewear with one set of lenses on the moving frame and another pair of lenses on a fixed frame (optional).
Glasses, c. 1920s, with springy cable temples
Modern glasses with a rectangular lens shape
Detail of a portrait of the Dominican Cardinal and renowned biblical scholar Hugh of Saint-Cher painted by Tommaso da Modena in 1352
Portrait of cardinal Fernando Niño de Guevara by El Greco circa 1600 shows glasses with temples passing over and beyond the ears
The Glasses Apostle by Conrad von Soest (1403)
Seated apostle holding lenses in position for reading. Detail from Death of the Virgin, by the Master of Heiligenkreuz, c. 1400–1430 (Getty Center).
French Empire gilt scissors glasses (with one lens missing), c. 1805
A portrait of Francisco de Quevedo y Villegas, 1580–1645
Harry S. Truman, 33rd President of the United States, had poor vision.
Woman wearing eyewear with non-prescription lenses in a fashion photo shoot.
Glasses - Decoration, Presi HQ, Budapest
Former United States senator Barry Goldwater in horn-rimmed glasses

The most common type of corrective lens is "single vision", which has a uniform refractive index.

Sunglasses provide more comfort and protection against bright light and often against ultraviolet (UV) light.

Pencils shown in various colors

Color

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Visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes.

Visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes.

Pencils shown in various colors
Continuous optical spectrum rendered into the sRGB color space.
The upper disk and the lower disk have exactly the same objective color, and are in identical gray surroundings; based on context differences, humans perceive the squares as having different reflectances, and may interpret the colors as different color categories; see checker shadow illusion.
Normalized typical human cone cell responses (S, M, and L types) to monochromatic spectral stimuli
The visual dorsal stream (green) and ventral stream (purple) are shown. The ventral stream is responsible for color perception.
This picture contains one million pixels, each one a different color
The CIE 1931 color space xy chromaticity diagram with the visual locus plotted using the CIE (2006) physiologically-relevant LMS fundamental color matching functions transformed into the CIE 1931 xy color space and converted into Adobe RGB. The triangle shows the gamut of Adobe RGB. The Planckian locus is shown with color temperatures labeled in Kelvins. The outer curved boundary is the spectral (or monochromatic) locus, with wavelengths shown in nanometers. Note that the colors in this file are being specified using Adobe RGB. Areas outside the triangle cannot be accurately rendered since they are outside the gamut of Adobe RGB, therefore they have been interpreted. Note that the colors depicted depend on the gamut and color accuracy of your display.
Additive color mixing: combining red and green yields yellow; combining all three primary colors together yields white.
Subtractive color mixing: combining yellow and magenta yields red; combining all three primary colors together yields black
Twelve main pigment colors

It includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what is commonly referred to simply as light).

The wavelengths listed are as measured in air or vacuum (see refractive index).

A photodetector salvaged from a CD-ROM drive. The photodetector contains three photodiodes, visible in the photo (in center).

Photodetector

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A photodetector salvaged from a CD-ROM drive. The photodetector contains three photodiodes, visible in the photo (in center).
A commercial amplified photodetector for use in optics research

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation.

Polarization: Photons induce changes in polarization states of suitable materials, which may lead to change in index of refraction or other polarization effects.

The reflection of Mount Hood in Mirror Lake.

Reflection (physics)

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Change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

Change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

The reflection of Mount Hood in Mirror Lake.
Diagram of specular reflection
Refraction of light at the interface between two media.
An example of the law of reflection
General scattering mechanism which gives diffuse reflection by a solid surface
Working principle of a corner reflector
Multiple reflections in two plane mirrors at a 60° angle.
Sound diffusion panel for high frequencies

Common examples include the reflection of light, sound and water waves.

In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index.

Laser light is a type of stimulated emission of radiation.

Stimulated emission

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Process by which an incoming photon of a specific frequency can interact with an excited atomic electron , causing it to drop to a lower energy level.

Process by which an incoming photon of a specific frequency can interact with an excited atomic electron , causing it to drop to a lower energy level.

Laser light is a type of stimulated emission of radiation.
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When an electron absorbs energy either from light (photons) or heat (phonons), it receives that incident quantum of energy.

n is the refractive index of the medium (dimensionless), and