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 Mathematical concept is that
Color Color (American English) or colour (British English; see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, blue, yellow, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects or materials based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates. Because perception of color stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. The science of color is sometimes called chromatics, colorimetry, or simply color science. Physics of color Perception
Covariant formulation of classical electromagnetism The covariant formulation of classical electromagnetism refers to ways of writing the laws of classical electromagnetism (in particular, Maxwell's equations and the Lorentz force) in a form that is manifestly invariant under Lorentz transformations, in the formalism of special relativity using rectilinear inertial coordinate systems. These expressions both make it simple to prove that the laws of classical electromagnetism take the same form in any inertial coordinate system, and also provide a way to translate the fields and forces from one frame to another. However, this is not as general as Maxwell's equations in curved spacetime or non-rectilinear coordinate systems. This article uses SI units for the purely spatial components of tensors (including vectors), the classical treatment of tensors and the Einstein summation convention throughout, and the Minkowski metric has the form diag (+1, −1, −1, −1). Covariant objects Preliminary 4-vectors In meter−1 the four-gradient is
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 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. Reflection 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 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 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). 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. Brief history of wave and particle viewpoints 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.
Visual appearance Appearance of reflective objects The appearance of reflecting objects is determined by the way the surface reflects incident light. The reflective properties of the surface can be characterized by a closer look at the (micro)-topography of that surface. Definition diffusion, scattering: process by which the spatial distribution of a beam of radiation is changed in many directions when it is deviated by a surface or by a medium, without change of frequency of its monochromatic components. Basic types of light reflection Appearance of transmissive objects Terminology Reflective objects  Transmissive objects  See also References Jump up ^ CIE No17.4-1987: International lighting vocabulary, 4th ed. F. External links Instrumentation for measurement and evaluation of appearance characteristics is available from:
Quantum mechanics Wavefunctions of the electron in a hydrogen atom at different energy levels. Quantum mechanics cannot predict the exact location of a particle in space, only the probability of finding it at different locations. The brighter areas represent a higher probability of finding the electron. Quantum mechanics (QM; also known as quantum physics, quantum theory, the wave mechanical model, or matrix mechanics), including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of atoms and subatomic particles. Quantum mechanics gradually arose from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's solution in 1900 to the black-body radiation problem, and from the correspondence between energy and frequency in Albert Einstein's 1905 paper which explained the photoelectric effect. History In 1838, Michael Faraday discovered cathode rays. where h is Planck's constant. Coulomb potential.
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. Ley de Snell[editar] Lentes[editar] Espejos[editar]
Photon Nomenclature 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  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. 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 The cone shows possible values of wave 4-vector of a photon. A photon is massless,[Note 2] has no electric charge, 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