A report on Light and Wavelength

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
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.
The electromagnetic spectrum, with the visible portion highlighted
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.
800px
A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue)
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
Wavelength is decreased in a medium with slower propagation.
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
Refraction: upon entering a medium where its speed is lower, the wave changes direction.
Hong Kong illuminated by colourful artificial lighting.
Separation of colors by a prism (click for animation)
Pierre Gassendi.
Various local wavelengths on a crest-to-crest basis in an ocean wave approaching shore
Christiaan Huygens.
A sinusoidal wave travelling in a nonuniform medium, with loss
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.
A wave on a line of atoms can be interpreted according to a variety of wavelengths.
400x400px
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.

Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).

- Light

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

- Wavelength
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

The electromagnetic spectrum

Electromagnetic spectrum

5 links

The electromagnetic spectrum
A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths
Plot of Earth's atmospheric opacity to various wavelengths of electromagnetic radiation. This is the surface-to-space opacity, the atmosphere is transparent to longwave radio transmissions within the troposphere but opaque to space due to the ionosphere.
Plot of atmospheric opacity for terrestrial to terrestrial transmission showing the molecules responsible for some of the resonances
The amount of penetration of UV relative to altitude in Earth's ozone

The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.

This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end.

400x400px

Electromagnetic radiation

4 links

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, propagating through space, carrying electromagnetic radiant energy.

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, propagating through space, carrying electromagnetic radiant energy.

400x400px
Shows the relative wavelengths of the electromagnetic waves of three different colours of light (blue, green, and red) with a distance scale in micrometers along the x-axis.
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power, so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation thus includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, forms part of the changing electromagnetic field, but does not count as electromagnetic radiation.
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. The electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
James Clerk Maxwell
Electromagnetic spectrum with visible light highlighted
Rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation

It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength.

White light is dispersed by a prism into the colors of the visible spectrum.

Visible spectrum

2 links

Portion of the electromagnetic spectrum that is visible to the human eye.

Portion of the electromagnetic spectrum that is visible to the human eye.

White light is dispersed by a prism into the colors of the visible spectrum.
Laser beams with visible spectrum
Newton's color circle, from Opticks of 1704, showing the colors he associated with musical notes. The spectral colors from red to violet are divided by the notes of the musical scale, starting at D. The circle completes a full octave, from D to D. Newton's circle places red, at one end of the spectrum, next to violet, at the other. This reflects the fact that non-spectral purple colors are observed when red and violet light are mixed.
Newton's observation of prismatic colors (David Brewster 1855)
How visible light interacts with objects to make them colorful
Approximation of spectral colors on a display results in somewhat distorted chromaticity
Earth's atmosphere partially or totally blocks some wavelengths of electromagnetic radiation, but in visible light it is mostly transparent

Electromagnetic radiation in this range of wavelengths is called visible light or simply light.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz

Frequency

2 links

Number of occurrences of a repeating event per unit of time.

Number of occurrences of a repeating event per unit of time.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz
A pendulum with a period of 2.8 s and a frequency of 0.36 Hz
Diagram of the relationship between the different types of frequency and other wave properties.
Modern frequency counter
Complete spectrum of electromagnetic radiation with the visible portion highlighted
The sound wave spectrum, with rough guide of some applications

Frequency is an important parameter used in science and engineering to specify the temporal rate of change observed in oscillatory and periodic phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

For periodic waves in nondispersive media (that is, media in which the wave speed is independent of frequency), frequency has an inverse relationship to the wavelength, λ (lambda).

A ray of light being refracted in a plastic block.

Refraction

2 links

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.

The refractive index of materials varies with the wavelength of light, and thus the angle of the refraction also varies correspondingly.

The spectrum in a rainbow

Spectrum

1 links

Condition that is not limited to a specific set of values but can vary, without gaps, across a continuum.

Condition that is not limited to a specific set of values but can vary, without gaps, across a continuum.

The spectrum in a rainbow
Diagram illustrating the electromagnetic spectrum
Mass spectrum of Titan's ionosphere
Spectrogram of dolphin vocalizations
A Nolan chart of the political spectrum using (red leftism and blue rightism) coding

The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism.

Soon the term referred to a plot of light intensity or power as a function of frequency or wavelength, also known as a spectral density plot.

Top to bottom: Lights flashing at frequencies, 1 Hz and 2 Hz; that is, at 0.5, 1.0 and 2.0 flashes per second, respectively. The time between each flash – the period T – is given by 1⁄f (the reciprocal of f); that is, 2, 1 and 0.5 seconds, respectively.

Hertz

2 links

Unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Top to bottom: Lights flashing at frequencies, 1 Hz and 2 Hz; that is, at 0.5, 1.0 and 2.0 flashes per second, respectively. The time between each flash – the period T – is given by 1⁄f (the reciprocal of f); that is, 2, 1 and 0.5 seconds, respectively.
A sine wave with varying frequency
A heartbeat is an example of a non-sinusoidal periodic phenomenon that may be analyzed in terms of frequency. Two cycles are illustrated.

Light is electromagnetic radiation that is even higher in frequency, and has frequencies in the range of tens (infrared) to thousands (ultraviolet) of terahertz.

(For historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies: for a more detailed treatment of this and the above frequency ranges, see electromagnetic spectrum.)

A ray of light being refracted in a plastic block

Refractive index

1 links

A ray of light being refracted in a plastic block
Refraction of a light ray
Thomas Young coined the term index of refraction.
Diamonds have a very high refractive index of 2.417.
A split-ring resonator array arranged to produce a negative index of refraction for microwaves
In optical mineralogy, thin sections are used to study rocks. The method is based on the distinct refractive indices of different minerals.
Light of different colors has slightly different refractive indices in water and therefore shows up at different positions in the rainbow.
In a prism, dispersion causes different colors to refract at different angles, splitting white light into a rainbow of colors.
The variation of refractive index with wavelength for various glasses. The shaded zone indicates the range of visible light.
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.

The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, and similarly the wavelength in that medium is λ = λ0/n, where λ0 is the wavelength of that light in vacuum.

The 100-inch (2.54 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, USA, used by Edwin Hubble to measure galaxy redshifts and discover the general expansion of the universe.

Telescope

1 links

Optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

Optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

The 100-inch (2.54 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, USA, used by Edwin Hubble to measure galaxy redshifts and discover the general expansion of the universe.
17th century telescope
The 60-inch Hale (debuted in 1908) considered to be the first modern large research reflecting telescope.
The primary mirror assembly of James Webb Space Telescope under construction. This is a segmented mirror and its coated with Gold to reflect (orange-red) visible light, through near-infrared to the mid-infrared
Modern telescopes typically use CCDs instead of film for recording images. This is the sensor array in the Kepler spacecraft.
A 1.2-meter (47 in) reflecting telescope
Binoculars
The Very Large Array at Socorro, New Mexico, United States.
Einstein Observatory was a space-based focusing optical X-ray telescope from 1978.
The Compton Gamma Ray Observatory is released into orbit by the Space Shutte in 1991, and it would operate until the year 2000
The reflectors of HEGRA detect flashes of light in the atmosphere, thus detecting high energy particles
Equatorial-mounted Keplerian telescope
A diagram of the electromagnetic spectrum with the Earth's atmospheric transmittance (or opacity) and the types of telescopes used to image parts of the spectrum.
Six views of the Crab nebula supernova remnant, viewed at different wavelengths of light by various telescopes
The Five-hundred-meter Aperture Spherical radio Telescope in Guizhou, China, is the world's largest filled-aperture radio telescope

Optical telescopes, using visible light

The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed.

The interference of two waves. When in phase, the two lower waves create constructive interference (left), resulting in a wave of greater amplitude. When 180° out of phase, they create destructive interference (right).

Wave interference

0 links

Phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

Phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

The interference of two waves. When in phase, the two lower waves create constructive interference (left), resulting in a wave of greater amplitude. When 180° out of phase, they create destructive interference (right).
Interference of right traveling (green) and left traveling (blue) waves in Two-dimensional space, resulting in final (red) wave
Interference of waves from two point sources.
A magnified image of a coloured interference pattern in a soap film. The "black holes" are areas of almost total destructive interference (antiphase).
Geometrical arrangement for two plane wave interference
Interference fringes in overlapping plane waves
Optical interference between two point sources that have different wavelengths and separations of sources.
Creation of interference fringes by an optical flat on a reflective surface. Light rays from a monochromatic source pass through the glass and reflect off both the bottom surface of the flat and the supporting surface.  The tiny gap between the surfaces means the two reflected rays have different path lengths. In addition the ray reflected from the bottom plate undergoes a 180° phase reversal.  As a result, at locations (a) where the path difference is an odd multiple of λ/2, the waves reinforce.   At locations (b) where the path difference is an even multiple of λ/2 the waves cancel.  Since the gap between the surfaces varies slightly in width at different points, a series of alternating bright and dark bands, interference fringes, are seen.
White light interference in a soap bubble. The iridescence is due to thin-film interference.
The Very Large Array, an interferometric array formed from many smaller telescopes, like many larger radio telescopes.

Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves.

The fringe spacing increases with increase in wavelength, and with decreasing angle