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Main article: Electromagnetic radiation A linearly polarized electromagnetic wave traveling along the z-axis, with E denoting the electric field and perpendicular B denoting magnetic field Light moves in a straight line. The straight line path is often drawn as a ray. Humans can only see rays of light traveling directly into the eyes. Ray diagrams are used to illustrate light traveling from one place to another. A beam of light can be thought of as a set of light rays. Use a protractor to measure angles of incidence from this normal of 10°, 20°, 30°, 40°, 50°, 60° and 70°. Draw in the incident rays corresponding to these angles and label them A, B, C.... Record these angles of incidence in a suitable table. Light with a wavelength shorter than violet is called ultraviolet light. X-rays and gamma rays are forms of light with even shorter wavelengths than ultraviolet. Light with a wavelength longer than red is called infrared light. Radio waves are a form of electromagnetic radiation with a wavelength longer than infrared light. The microwaves that are used to heat food in a microwave oven are also a form of electromagnetic radiation. Our eyes cannot see those kinds of energy, but there are some cameras that can see them. The various forms of light, both visible and invisible are the electromagnetic spectrum.

a b c "Shastra Pratibha 2015 Seniors Booklet" (PDF). Sifuae.com. Archived from the original (PDF) on 30 May 2015 . Retrieved 29 August 2017. Light transmits spatial and temporal information. This property forms the basis of the fields of optics and optical communications and a myriad of related technologies, both mature and emerging. Technological applications based on the manipulations of light include lasers, holography, and fibre-optic telecommunications systems. Generally, electromagnetic radiation (EMR) is classified by wavelength into radio waves, microwaves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays and gamma rays. The designation " radiation" excludes static electric, magnetic and near fields. With the pencil mark two Xs to indicate the direction of the emergent ray. Mark the Xs as far apart as possible.The other main properties of light are intensity, polarization, phase and orbital angular momentum.

Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is used in cathode-ray tube television sets and computer monitors. The fact that light could be polarized was for the first time qualitatively explained by Newton using the particle theory. Étienne-Louis Malus in 1810 created a mathematical particle theory of polarization. Jean-Baptiste Biot in 1812 showed that this theory explained all known phenomena of light polarization. At that time the polarization was considered as the proof of the particle theory.

In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. [2] [3] This article is about visible light. Read the electromagnetic radiation article for the general concept. Light is a form of electromagnetic radiation. It is the natural agent that stimulates sight and makes things easy to see. Visible light" redirects here. For all parts of the electromagnetic spectrum that can be seen by the eye, see Visible spectrum. a b Newcomb, Simon (1911). "Light" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 16 (11th ed.). Cambridge University Press. p. 624.

The photometry units are different from most systems of physical units in that they take into account how the human eye responds to light. The cone cells in the human eye are of three types which respond differently across the visible spectrum and the cumulative response peaks at a wavelength of around 555 nm. Therefore, two sources of light which produce the same intensity (W/m 2) of visible light do not necessarily appear equally bright. The photometry units are designed to take this into account and therefore are a better representation of how "bright" a light appears to be than raw intensity. They relate to raw power by a quantity called luminous efficacy and are used for purposes like determining how to best achieve sufficient illumination for various tasks in indoor and outdoor settings. The illumination measured by a photocell sensor does not necessarily correspond to what is perceived by the human eye and without filters which may be costly, photocells and charge-coupled devices (CCD) tend to respond to some infrared, ultraviolet or both.The effective velocity of light in various transparent substances containing ordinary matter, is less than in vacuum. For example, the speed of light in water is about 3/4 of that in vacuum. Berns, Roy S. (2019). Billmeyer and Saltzman's Principles of Color Technology. Fred W. Billmeyer, Max Saltzman (4th ed.). Hoboken, NJ: Wiley. ISBN 978-1-119-36668-3. OCLC 1080250734. The wave theory predicted that light waves could interfere with each other like sound waves (as noted around 1800 by Thomas Young). Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colours were caused by different wavelengths of light and explained colour vision in terms of three-coloured receptors in the eye. Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory. In 1816 André-Marie Ampère gave Augustin-Jean Fresnel an idea that the polarization of light can be explained by the wave theory if light were a transverse wave. [37]

Eventually the modern theory of quantum mechanics came to picture light as (in some sense) both a particle and a wave and (in another sense), as a phenomenon which is neither a particle nor a wave (which actually are macroscopic phenomena, such as baseballs or ocean waves). Instead, modern physics sees light as something that can be described sometimes with mathematics appropriate to one type of macroscopic metaphor (particles) and sometimes another macroscopic metaphor (water waves), but is actually something that cannot be fully imagined. As in the case for radio waves and the X-rays involved in Compton scattering, physicists have noted that electromagnetic radiation tends to behave more like a classical wave at lower frequencies, but more like a classical particle at higher frequencies, but never completely loses all qualities of one or the other. Visible light, which occupies a middle ground in frequency, can easily be shown in experiments to be describable using either a wave or particle model, or sometimes both. Dash, Madhab Chandra; Dash, Satya Prakash (2009). Fundamentals of Ecology 3E. Tata McGraw-Hill Education. p. 213. ISBN 978-1-259-08109-5. Archived from the original on 8 October 2022 . Retrieved 18 October 2013. Normally the human eye responds to light rays from 390 to 760 nm. This can be extended to a range of 310 to 1,050 nm under artificial conditions.

Video transcript for ‘Light’

When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as refraction. James R. Hofmann, André-Marie Ampère: Enlightenment and Electrodynamics, Cambridge University Press, 1996, p. 222. Svitil, Kathy A. (5 February 2004). "Asteroids Get Spun By the Sun". Discover Magazine. Archived from the original on 9 October 2012 . Retrieved 8 May 2007. Although the motion of the Crookes radiometer was originally attributed to light pressure, this interpretation is incorrect; the characteristic Crookes rotation is the result of a partial vacuum. [27] This should not be confused with the Nichols radiometer, in which the (slight) motion caused by torque (though not enough for full rotation against friction) is directly caused by light pressure. [28] Various sources define visible light as narrowly as 420–680 nm [7] [8] to as broadly as 380–800 nm. [9] [10] Under ideal laboratory conditions, people can see infrared up to at least 1,050 nm; [11] children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm. [12] [13] [14]