Spacetime In non-relativistic classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer.[disambiguation needed] In relativistic contexts, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer and also on the strength of gravitational fields, which can slow the passage of time for an object as seen by an observer outside the field. Until the beginning of the 20th century, time was believed to be independent of motion, progressing at a fixed rate in all reference frames; however, later experiments revealed that time slows at higher speeds of the reference frame relative to another reference frame. Such slowing, called time dilation, is explained in special relativity theory. Spacetime in literature[edit] Mathematical concept[edit] is that
Geometrical optics The simplifying assumptions of geometrical optics include that light rays: propagate in rectilinear paths as they travel in a homogeneous mediumbend, and in particular circumstances may split in two, at the interface between two dissimilar mediafollow curved paths in a medium in which the refractive index changesmay be absorbed or reflected. Explanation[edit] A slightly more rigorous definition of a light ray follows from Fermat's principle, which states that the path taken between two points by a ray of light is the path that can be traversed in the least time.[1] Reflection[edit] Glossy surfaces such as mirrors reflect light in a simple, predictable way. With such surfaces, the direction of the reflected ray is determined by the angle the incident ray makes with the surface normal, a line perpendicular to the surface at the point where the ray hits. Refraction[edit] Illustration of Snell's Law and another medium with index of refraction . where and ) and object distance ( varies slowly. . with
Wave–particle duality Origin of theory[edit] The idea of duality originated in a debate over the nature of light and matter that dates back to the 17th century, when Christiaan Huygens and Isaac Newton proposed competing theories of light: light was thought either to consist of waves (Huygens) or of particles (Newton). Through the work of Max Planck, Albert Einstein, Louis de Broglie, Arthur Compton, Niels Bohr, and many others, current scientific theory holds that all particles also have a wave nature (and vice versa).[2] This phenomenon has been verified not only for elementary particles, but also for compound particles like atoms and even molecules. For macroscopic particles, because of their extremely short wavelengths, wave properties usually cannot be detected.[3] Brief history of wave and particle viewpoints[edit] Thomas Young's sketch of two-slit diffraction of waves, 1803 Particle impacts make visible the interference pattern of waves. A quantum particle is represented by a wave packet.
Óptica geométrica Formación de un arco iris por medio de la óptica geométrica. La óptica geométrica usa la noción de rayo luminoso; es una aproximación del comportamiento que corresponde a las ondas electromagnéticas (la luz) cuando los objetos involucrados son de tamaño mucho mayor que la longitud de onda usada; ello permite despreciar los efectos derivados de la difracción, comportamiento ligado a la naturaleza ondulatoria de la luz. Esta aproximación es llamada de la Eikonal y permite derivar la óptica geométrica a partir de algunas de las ecuaciones de Maxwell. Propagación de la luz[editar] Reflexión y refracción[editar] El fenómeno más sencillo de esta teoría es la de la reflexión, si pensamos unos minutos en los rayos luminosos que chocan mecánicamente contra una superficie que puede reflejarse. La segunda ley de la reflexión nos indica que el rayo incidente, el rayo reflejado y la normal con respecto a la superficie reflejada están en el mismo plano.[2] Ley de Snell[editar] Lentes[editar] Espejos[editar]
Photon Nomenclature[edit] In 1900, Max Planck was working on black-body radiation and suggested that the energy in electromagnetic waves could only be released in "packets" of energy. In his 1901 article [4] in Annalen der Physik he called these packets "energy elements". The word quanta (singular quantum) was used even before 1900 to mean particles or amounts of different quantities, including electricity. Later, in 1905, Albert Einstein went further by suggesting that electromagnetic waves could only exist in these discrete wave-packets.[5] He called such a wave-packet the light quantum (German: das Lichtquant). The name photon derives from the Greek word for light, φῶς (transliterated phôs). Physical properties[edit] The cone shows possible values of wave 4-vector of a photon. A photon is massless,[Note 2] has no electric charge,[13] and is stable. Photons are emitted in many natural processes. Since p points in the direction of the photon's propagation, the magnitude of the momentum is
Luz Se llama luz (del latín lux, lucis) a la parte de la radiación electromagnética que puede ser percibida por el ojo humano. En física, el término luz se usa en un sentido más amplio e incluye todo el campo de la radiación conocido como espectro electromagnético, mientras que la expresión luz visible señala específicamente la radiación en el espectro visible. La óptica es la rama de la física que estudia el comportamiento de la luz, sus características y sus manifestaciones. El estudio de la luz revela una serie de características y efectos al interactuar con la materia, que permiten desarrollar algunas teorías sobre su naturaleza. En el 55 A.C., Lucrecio, un poeta romano atomista, escribió: "La luz y calor del sol; Estas están compuestas de átomos diminutos que, cuando se metieron, no pierden ningún tiempo en el tiroteo intermedio del aire en la dirección impartida por el empujón. –" De rerum natura Velocidad finita[editar] Refracción[editar] Ejemplo de la refracción. Interferencia[editar]
Thermal radiation This diagram shows how the peak wavelength and total radiated amount vary with temperature according to Wien's displacement law. Although this plot shows relatively high temperatures, the same relationships hold true for any temperature down to absolute zero. Visible light is between 380 and 750 nm. Thermal radiation in visible light can be seen on this hot metalwork. Its emission in the infrared is invisible to the human eye and the camera the image was taken with, but an infrared camera could show it (See Thermography). Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. Examples of thermal radiation include the visible light and infrared light emitted by an incandescent light bulb, the infrared radiation emitted by animals and detectable with an infrared camera, and the cosmic microwave background radiation. Thermal radiation is one of the fundamental mechanisms of heat transfer. Overview[edit] Surface effects[edit] Here,
History of optics Early history of optics[edit] Some lenses fixed in ancient Egyptian statues are much older than those mentioned above. There is some doubt as to whether or not they qualify as lenses, but they are undoubtedly glass and served at least ornamental purposes. The statues appear to be anatomically correct schematic eyes.[citation needed] In ancient India, the philosophical schools of Samkhya and Vaisheshika, from around the 6th–5th century BC, developed theories on light. In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. In his Optics Greek mathematician Euclid observed that "things seen under a greater angle appear greater, and those under a lesser angle less, while those under equal angles appear equal". In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote: The beginnings of geometrical optics[edit] Optics and vision in the Islamic world[edit] Optics in medieval Europe[edit] See also[edit]
Absolute zero Absolute zero is the lower limit of the thermodynamic temperature scale, a ficticious state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15° on the Celsius scale (International System of Units),[1][2] which equates to −459.67° on the Fahrenheit scale (English/United States customary units).[3] The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition. The laws of thermodynamics dictate that absolute zero cannot be reached using only thermodynamic means,[clarification needed] as the temperature of the substance being cooled approaches the temperature of the cooling agent asymptotically. A system at absolute zero still possesses quantum mechanical zero-point energy, the energy of its ground state. The kinetic energy of the ground state cannot be removed.