232 relations: Abraham–Lorentz force, Absorption spectroscopy, Active Denial System, Albert Einstein, Allen Taflove, Allotropes of oxygen, Alpha particle, Alternating current, Angular momentum, Antenna (radio), Antenna measurement, Atom, Atomic electron transition, Beta particle, Bioelectromagnetics, Black body, Black-body radiation, Blacklight, Bolometer, Bremsstrahlung, Cambridge University Press, Carotenoid, Cartesian coordinate system, Cavity magnetron, Charged particle, Chemical bond, Chemical element, Chemical reaction, Chlorophyll, Classical electromagnetism, Compton scattering, CONELRAD, Conservation of energy, Crystal, Curl (mathematics), D'Alembert operator, Death ray, Del, Density, Differential equation, Diffraction, Dispersion (optics), Dispersion relation, Dispersive prism, DNA, Ear, Edward Andrade, Electric current, Electric dipole moment, Electric field, ..., Electrical conductor, Electrical reactance, Electricity, Electromagnetic field, Electromagnetic induction, Electromagnetic interference, Electromagnetic pulse, Electromagnetic radiation and health, Electromagnetic spectrum, Electromagnetic wave equation, Electromagnetism, Electron, Electronvolt, Electrostatic induction, Elementary particle, Emission spectrum, Energy, Energy level, Entropy, Ernest Rutherford, Euclidean vector, Evanescent field, Excited state, Faraday effect, Finite-difference time-domain method, First quantization, Fluorescence, Fourier analysis, Frequency, Gamma ray, George Francis FitzGerald, Gravitational wave, Harry Grindell Matthews, Health effects of sunlight exposure, Heat, Heinrich Hertz, Helicon (physics), Hendrik Lorentz, Henri Becquerel, Hertz, History of special relativity, Human eye, Impedance of free space, Infrared, Infrared sensing in snakes, Intensity (physics), Interferometry, International System of Units, Invariant mass, Inverse-square law, Ion, Ionization, Ionizing radiation, Ionosphere, James Clerk Maxwell, James Jeans, Johann Wilhelm Ritter, Kerr effect, Khan Academy, Laser, Liénard–Wiechert potential, Light, List of IARC Group 2B carcinogens, Louis de Broglie, Luminiferous aether, Magnetic dipole, Magnetic field, Marie Curie, Matter, Max Planck, Maxwell's equations, Mechanistic organic photochemistry, Metal detector, Microwave, Microwave oven, Momentum, Monochrome, Nanometre, Near and far field, Nebula, Nitrogen, Non-ionizing radiation, Non-photochemical quenching, Nonlinear optics, Oscillation, Ozone, Partial derivative, Paul Ulrich Villard, Phase (waves), Phosphorescence, Photochemistry, Photoelectric effect, Photoionization, Photoluminescence, Photomultiplier, Photon, Photon polarization, Photosynthesis, Photovoltaic effect, Physics, Planck constant, Planck energy, Planck's law, Planck–Einstein relation, Point source, Polarization (waves), Power (physics), Power density, Poynting vector, Prism, Proton, Pyrimidine dimer, Quantization (physics), Quantum, Quantum electrodynamics, Quantum mechanics, Radiant energy, Radical (chemistry), Radio wave, Radio-frequency induction, Radioactive decay, Radium, Reactive oxygen species, Red, Redshift, Refraction, Refractive index, Retina, Retinal, Rhodopsin, Royal Society, Rudolf Kohlrausch, Second, Shortwave radio, Silver chloride, Sine wave, Sinusoidal plane-wave solutions of the electromagnetic wave equation, Skywave, Snell's law, Special relativity, Spectral density, Speed of light, Sphere, Star, Stationary state, Stochastic process, Subatomic particle, Sun, Superposition principle, Symmetry (physics), Thermal energy, Thermal equilibrium, Thermal radiation, Thermometer, Transformer, Transverse wave, Ultraviolet, Ultraviolet catastrophe, Uranium, Vacuum, Vacuum permeability, Vacuum permittivity, Vacuum state, Vector calculus identities, Velocity, Velocity factor, Visible spectrum, Visual system, Voltage, Walter Lewin, Wave equation, Wave interference, Wave–particle duality, Wavefront, Wavelength, Wilhelm Eduard Weber, Wilhelm Röntgen, William Henry Bragg, William Herschel, World Health Organization, X-ray, 19th century. Expand index (182 more) » « Shrink index
In the physics of electromagnetism, the Abraham–Lorentz force (also Lorentz–Abraham force) is the recoil force on an accelerating charged particle caused by the particle emitting electromagnetic radiation.
Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample.
The Active Denial System (ADS) is a non-lethal, directed-energy weapon developed by the U.S. military, designed for area denial, perimeter security and crowd control.
Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).
Allen Taflove is a full professor in the Department of Electrical Engineering and Computer Science of Northwestern's McCormick School of Engineering, since 1988.
There are several known allotropes of oxygen.
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus.
Alternating current (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction.
In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum.
In radio, an antenna is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.
Antenna measurement techniques refers to the testing of antennas to ensure that the antenna meets specifications or simply to characterize it.
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.
Atomic electron transition is a change of an electron from one energy level to another within an atom or artificial atom.
A beta particle, also called beta ray or beta radiation, (symbol β) is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay.
Bioelectromagnetics, also known as bioelectromagnetism, is the study of the interaction between electromagnetic fields and biological entities.
A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.
Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body).
A blacklight (or often black light), also referred to as a UV-A light, Wood's lamp, or simply ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and not much visible light.
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance.
Bremsstrahlung, from bremsen "to brake" and Strahlung "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus.
Cambridge University Press (CUP) is the publishing business of the University of Cambridge.
Carotenoids, also called tetraterpenoids, are organic pigments that are produced by plants and algae, as well as several bacteria and fungi.
A Cartesian coordinate system is a coordinate system that specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular directed lines, measured in the same unit of length.
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators).
In physics, a charged particle is a particle with an electric charge.
A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds.
A chemical element is a species of atoms having the same number of protons in their atomic nuclei (that is, the same atomic number, or Z).
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.
Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and the chloroplasts of algae and plants.
Classical electromagnetism or classical electrodynamics is a branch of theoretical physics that studies the interactions between electric charges and currents using an extension of the classical Newtonian model.
Compton scattering, discovered by Arthur Holly Compton, is the scattering of a photon by a charged particle, usually an electron.
CONELRAD (Control of Electromagnetic Radiation) was a method of emergency broadcasting to the public of the United States in the event of enemy attack during the Cold War.
In physics, the law of conservation of energy states that the total energy of an isolated system remains constant, it is said to be ''conserved'' over time.
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.
In vector calculus, the curl is a vector operator that describes the infinitesimal rotation of a vector field in three-dimensional Euclidean space.
In special relativity, electromagnetism and wave theory, the d'Alembert operator (represented by a box: \Box), also called the d'Alembertian, wave operator, or box operator is the Laplace operator of Minkowski space.
The death ray or death beam was a theoretical particle beam or electromagnetic weapon of the 1920s and 1930s that was claimed to have been invented independently by Guglielmo Marconi, Nikola Tesla, Harry Grindell Matthews, Edwin R. Scott, and Graichen, as well as others.
Del, or nabla, is an operator used in mathematics, in particular in vector calculus, as a vector differential operator, usually represented by the nabla symbol ∇.
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume.
A differential equation is a mathematical equation that relates some function with its derivatives.
--> Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit.
In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency.
In physical sciences and electrical engineering, dispersion relations describe the effect of dispersion in a medium on the properties of a wave traveling within that medium.
In optics, a dispersive prism is an optical prism, usually having the shape of a geometrical triangular prism, used as a spectroscopic component.
Deoxyribonucleic acid (DNA) is a thread-like chain of nucleotides carrying the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses.
The ear is the organ of hearing and, in mammals, balance.
Edward Neville da Costa Andrade FRS (27 December 1887 – 6 June 1971) was an English physicist, writer, and poet.
An electric current is a flow of electric charge.
The electric dipole moment is a measure of the separation of positive and negative electrical charges within a system, that is, a measure of the system's overall polarity.
An electric field is a vector field surrounding an electric charge that exerts force on other charges, attracting or repelling them.
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of an electrical current in one or more directions.
In electrical and electronic systems, reactance is the opposition of a circuit element to a change in current or voltage, due to that element's inductance or capacitance.
Electricity is the set of physical phenomena associated with the presence and motion of electric charge.
An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.
Electromagnetic or magnetic induction is the production of an electromotive force (i.e., voltage) across an electrical conductor in a changing magnetic field.
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.
An electromagnetic pulse (EMP), also sometimes called a transient electromagnetic disturbance, is a short burst of electromagnetic energy.
Electromagnetic radiation can be classified into two types: ionizing radiation and non-ionizing radiation, based on the capability of a single photon with more than 10 eV energy to ionize oxygen or break chemical bonds.
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic wave equation is a second-order partial differential equation that describes the propagation of electromagnetic waves through a medium or in a vacuum.
Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles.
The electron is a subatomic particle, symbol or, whose electric charge is negative one elementary charge.
In physics, the electronvolt (symbol eV, also written electron-volt and electron volt) is a unit of energy equal to approximately joules (symbol J).
Electrostatic induction, also known as "electrostatic influence" or simply "influence" in Europe and Latin America, is a redistribution of electrical charge in an object, caused by the influence of nearby charges.
In particle physics, an elementary particle or fundamental particle is a particle with no substructure, thus not composed of other particles.
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state.
In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.
A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy.
In statistical mechanics, entropy is an extensive property of a thermodynamic system.
Ernest Rutherford, 1st Baron Rutherford of Nelson, HFRSE LLD (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist who came to be known as the father of nuclear physics.
In mathematics, physics, and engineering, a Euclidean vector (sometimes called a geometric or spatial vector, or—as here—simply a vector) is a geometric object that has magnitude (or length) and direction.
In electromagnetics, an evanescent field, or evanescent wave, is an oscillating electric and/or magnetic field that does not propagate as an electromagnetic wave but whose energy is spatially concentrated in the vicinity of the source (oscillating charges and currents).
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum).
In physics, the Faraday effect or Faraday rotation is a magneto-optical phenomenon—that is, an interaction between light and a magnetic field in a medium.
Finite-difference time-domain or Yee's method (named after the Chinese American applied mathematician Kane S. Yee, born 1934) is a numerical analysis technique used for modeling computational electrodynamics (finding approximate solutions to the associated system of differential equations).
A first quantization of a physical system is a semi-classical treatment of quantum mechanics, in which particles or physical objects are treated using quantum wave functions but the surrounding environment (for example a potential well or a bulk electromagnetic field or gravitational field) is treated classically.
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In mathematics, Fourier analysis is the study of the way general functions may be represented or approximated by sums of simpler trigonometric functions.
Frequency is the number of occurrences of a repeating event per unit of time.
A gamma ray or gamma radiation (symbol γ or \gamma), is penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei.
Prof George Francis FitzGerald FRS FRSE (3 August 1851 – 22 February 1901) was an Irish professor of "natural and experimental philosophy" (i.e., physics) at Trinity College in Dublin, Ireland, during the last quarter of the 19th century.
Gravitational waves are the disturbance in the fabric ("curvature") of spacetime generated by accelerated masses and propagate as waves outward from their source at the speed of light.
Harry Grindell Matthews (17 March 1880 – 11 September 1941) was an English inventor who claimed to have invented a death ray in the 1920s.
The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a principal source of vitamin D3 and a mutagen.
In thermodynamics, heat is energy transferred from one system to another as a result of thermal interactions.
Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell's electromagnetic theory of light.
A helicon is a low frequency electromagnetic wave that can exist in plasmas in the presence of a magnetic field.
Hendrik Antoon Lorentz (18 July 1853 – 4 February 1928) was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and theoretical explanation of the Zeeman effect.
Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a French physicist, Nobel laureate, and the first person to discover evidence of radioactivity.
The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.
The history of special relativity consists of many theoretical results and empirical findings obtained by Albert A. Michelson, Hendrik Lorentz, Henri Poincaré and others.
The human eye is an organ which reacts to light and pressure.
The impedance of free space,, is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space.
Infrared radiation (IR) is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye (although IR at wavelengths up to 1050 nm from specially pulsed lasers can be seen by humans under certain conditions). It is sometimes called infrared light.
The ability to sense infrared thermal radiation evolved independently in several different families of snakes.
In physics, intensity is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy.
Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information.
The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.
The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system.
The inverse-square law, in physics, is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity.
An ion is an atom or molecule that has a non-zero net electrical charge (its total number of electrons is not equal to its total number of protons).
Ionization or ionisation, is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes.
Ionizing radiation (ionising radiation) is radiation that carries enough energy to liberate electrons from atoms or molecules, thereby ionizing them.
The ionosphere is the ionized part of Earth's upper atmosphere, from about to altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere.
James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish scientist in the field of mathematical physics.
Sir James Hopwood Jeans (11 September 187716 September 1946) was an English physicist, astronomer and mathematician.
Johann Wilhelm Ritter (16 December 1776 – 23 January 1810) was a German chemist, physicist and philosopher.
The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field.
Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with a goal of creating a set of online tools that help educate students.
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
Liénard–Wiechert potentials describe the classical electromagnetic effect of a moving electric point charge in terms of a vector potential and a scalar potential in the Lorenz gauge.
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
Substances, mixtures and exposure circumstances in this list have been classified by the International Agency for Research on Cancer (IARC) as Group 2B: The agent (mixture) is "possibly carcinogenic to humans".
Louis Victor Pierre Raymond de Broglie, duke de Broglie (or; 15 August 1892 – 19 March 1987) was a French physicist who made groundbreaking contributions to quantum theory.
In the late 19th century, luminiferous aether or ether ("luminiferous", meaning "light-bearing"), was the postulated medium for the propagation of light.
A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the dimensions of the source are reduced to zero while keeping the magnetic moment constant.
A magnetic field is a vector field that describes the magnetic influence of electrical currents and magnetized materials.
Marie Skłodowska Curie (born Maria Salomea Skłodowska; 7 November 18674 July 1934) was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity.
In the classical physics observed in everyday life, matter is any substance that has mass and takes up space by having volume.
Max Karl Ernst Ludwig Planck, FRS (23 April 1858 – 4 October 1947) was a German theoretical physicist whose discovery of energy quanta won him the Nobel Prize in Physics in 1918.
Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.
Mechanistic organic photochemistry is that aspect of organic photochemistry which seeks to explain the mechanisms of organic photochemical reactions.
A metal detector is an electronic instrument which detects the presence of metal nearby.
Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter; with frequencies between and.
A microwave oven (also commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range.
In Newtonian mechanics, linear momentum, translational momentum, or simply momentum (pl. momenta) is the product of the mass and velocity of an object.
Monochrome describes paintings, drawings, design, or photographs in one color or values of one color.
The nanometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth (short scale) of a metre (m).
The near field and far field are regions of the electromagnetic field (EM) around an object, such as a transmitting antenna, or the result of radiation scattering off an object.
A nebula (Latin for "cloud" or "fog"; pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases.
Nitrogen is a chemical element with symbol N and atomic number 7.
Non-ionizing (or non-ionising) radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum (photon energy) to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule.
Non-photochemical quenching (NPQ) is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity.
Nonlinear optics (NLO) is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light.
Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states.
Ozone, or trioxygen, is an inorganic molecule with the chemical formula.
In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary).
Paul Ulrich Villard (28 September 1860 – 13 January 1934) was a French chemist and physicist.
Phase is the position of a point in time (an instant) on a waveform cycle.
Phosphorescence is a type of photoluminescence related to fluorescence.
Photochemistry is the branch of chemistry concerned with the chemical effects of light.
The photoelectric effect is the emission of electrons or other free carriers when light shines on a material.
Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.
Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation).
Photomultiplier tubes (photomultipliers or PMTs for short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum.
The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles).
Photon polarization is the quantum mechanical description of the classical polarized sinusoidal plane electromagnetic wave.
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities (energy transformation).
The photovoltaic effect is the creation of voltage and electric current in a material upon exposure to light and is a physical and chemical property/phenomenon.
Physics (from knowledge of nature, from φύσις phýsis "nature") is the natural science that studies matterAt the start of The Feynman Lectures on Physics, Richard Feynman offers the atomic hypothesis as the single most prolific scientific concept: "If, in some cataclysm, all scientific knowledge were to be destroyed one sentence what statement would contain the most information in the fewest words? I believe it is that all things are made up of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another..." and its motion and behavior through space and time and that studies the related entities of energy and force."Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events." Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves."Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physics. (...) You will come to see physics as a towering achievement of the human intellect in its quest to understand our world and ourselves."Physics is an experimental science. Physicists observe the phenomena of nature and try to find patterns that relate these phenomena.""Physics is the study of your world and the world and universe around you." Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Over the last two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the scientific revolution in the 17th century, these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in academic disciplines such as mathematics and philosophy. Advances in physics often enable advances in new technologies. For example, advances in the understanding of electromagnetism and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.
The Planck constant (denoted, also called Planck's constant) is a physical constant that is the quantum of action, central in quantum mechanics.
In physics, Planck energy, denoted by, is the unit of energy in the system of natural units known as Planck units.
Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. The law is named after Max Planck, who proposed it in 1900.
The Planck–Einstein relationFrench & Taylor (1978), pp.
A point source is a single identifiable localised source of something.
Polarization (also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations.
In physics, power is the rate of doing work, the amount of energy transferred per unit time.
Power density (or volume power density or volume specific power) is the amount of power (time rate of energy transfer) per unit volume.
In physics, the Poynting vector represents the directional energy flux (the energy transfer per unit area per unit time) of an electromagnetic field.
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light.
Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions.
In physics, quantization is the process of transition from a classical understanding of physical phenomena to a newer understanding known as quantum mechanics.
In physics, a quantum (plural: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction.
In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics.
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 energy levels of atoms and subatomic particles.
In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic and gravitational radiation.
In chemistry, a radical (more precisely, a free radical) is an atom, molecule, or ion that has an unpaired valence electron.
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light.
Radio-frequency induction or RF induction is the use of a radio frequency magnetic field to transfer energy by means of electromagnetic induction in the near field.
Radioactive decay (also known as nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, gamma ray, or electron in the case of internal conversion.
Radium is a chemical element with symbol Ra and atomic number 88.
Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen.
Red is the color at the end of the visible spectrum of light, next to orange and opposite violet.
In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.
Refraction is the change in direction of wave propagation due to a change in its transmission medium.
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium.
The retina is the innermost, light-sensitive "coat", or layer, of shell tissue of the eye of most vertebrates and some molluscs.
Retinal is also known as retinaldehyde.
Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction.
The President, Council and Fellows of the Royal Society of London for Improving Natural Knowledge, commonly known as the Royal Society, is a learned society.
Rudolf Hermann Arndt Kohlrausch (November 6, 1809 in Göttingen – March 8, 1858 in Erlangen) was a German physicist.
The second is the SI base unit of time, commonly understood and historically defined as 1/86,400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.
Shortwave radio is radio transmission using shortwave radio frequencies.
Silver chloride is a chemical compound with the chemical formula AgCl.
A sine wave or sinusoid is a mathematical curve that describes a smooth periodic oscillation.
Sinusoidal plane-wave solutions are particular solutions to the electromagnetic wave equation.
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere.
Snell's law (also known as Snell–Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.
In physics, special relativity (SR, also known as the special theory of relativity or STR) is the generally accepted and experimentally well-confirmed physical theory regarding the relationship between space and time.
The power spectrum S_(f) of a time series x(t) describes the distribution of power into frequency components composing that signal.
The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.
A sphere (from Greek σφαῖρα — sphaira, "globe, ball") is a perfectly round geometrical object in three-dimensional space that is the surface of a completely round ball (viz., analogous to the circular objects in two dimensions, where a "circle" circumscribes its "disk").
A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.
A stationary state is a quantum state with all observables independent of time.
--> In probability theory and related fields, a stochastic or random process is a mathematical object usually defined as a collection of random variables.
In the physical sciences, subatomic particles are particles much smaller than atoms.
The Sun is the star at the center of the Solar System.
In physics and systems theory, the superposition principle, also known as superposition property, states that, for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually.
In physics, a symmetry of a physical system is a physical or mathematical feature of the system (observed or intrinsic) that is preserved or remains unchanged under some transformation.
Thermal energy is a term used loosely as a synonym for more rigorously-defined thermodynamic quantities such as the internal energy of a system; heat or sensible heat, which are defined as types of transfer of energy (as is work); or for the characteristic energy of a degree of freedom in a thermal system kT, where T is temperature and k is the Boltzmann constant.
Two physical systems are in thermal equilibrium if there are no net flow of thermal energy between them when they are connected by a path permeable to heat.
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter.
A thermometer is a device that measures temperature or a temperature gradient.
A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.
A transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave).
Ultraviolet (UV) is electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays.
The ultraviolet catastrophe, also called the Rayleigh–Jeans catastrophe, was the prediction of late 19th century/early 20th century classical physics that an ideal black body at thermal equilibrium will emit radiation in all frequency ranges, emitting more energy as the frequency increases.
Uranium is a chemical element with symbol U and atomic number 92.
Vacuum is space devoid of matter.
The physical constant μ0, (pronounced "mu naught" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is an ideal, (baseline) physical constant, which is the value of magnetic permeability in a classical vacuum.
The physical constant (pronounced as "epsilon nought"), commonly called the vacuum permittivity, permittivity of free space or electric constant, is an ideal, (baseline) physical constant, which is the value of the absolute dielectric permittivity of classical vacuum.
In quantum field theory, the quantum vacuum state (also called the quantum vacuum or vacuum state) is the quantum state with the lowest possible energy.
The following identities are important in vector calculus.
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.
The velocity factor (VF), also called wave propagation speed or velocity of propagation (VoP or of a transmission medium is the ratio of the speed at which a wavefront (of an electromagnetic signal, a radio signal, a light pulse in an optical fibre or a change of the electrical voltage on a copper wire) passes through the medium, to the speed of light in a vacuum.
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye.
The visual system is the part of the central nervous system which gives organisms the ability to process visual detail, as well as enabling the formation of several non-image photo response functions.
Voltage, electric potential difference, electric pressure or electric tension (formally denoted or, but more often simply as V or U, for instance in the context of Ohm's or Kirchhoff's circuit laws) is the difference in electric potential between two points.
Walter Hendrik Gustav Lewin (born January 29, 1936) is a Dutch astrophysicist and former professor of physics at the Massachusetts Institute of Technology.
The wave equation is an important second-order linear partial differential equation for the description of waves—as they occur in classical physics—such as mechanical waves (e.g. water waves, sound waves and seismic waves) or light waves.
In physics, interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude.
Wave–particle duality is the concept in quantum mechanics that every particle or quantic entity may be partly described in terms not only of particles, but also of waves.
In physics, a wavefront is the locus of points characterized by propagation of positions of identical phase: propagation of a point in 1D, a curve in 2D or a surface in 3D.
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
Wilhelm Eduard Weber (24 October 1804 – 23 June 1891) was a German physicist and, together with Carl Friedrich Gauss, inventor of the first electromagnetic telegraph.
Wilhelm Conrad Röntgen (27 March 1845 – 10 February 1923) was a German mechanical engineer and physicist, who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range known as X-rays or Röntgen rays, an achievement that earned him the first Nobel Prize in Physics in 1901.
Sir William Henry Bragg (2 July 1862 – 12 March 1942) was a British physicist, chemist, mathematician and active sportsman who uniquelyThis is still a unique accomplishment, because no other parent-child combination has yet shared a Nobel Prize (in any field).
Frederick William Herschel, (Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer, composer and brother of fellow astronomer Caroline Herschel, with whom he worked.
The World Health Organization (WHO; French: Organisation mondiale de la santé) is a specialized agency of the United Nations that is concerned with international public health.
X-rays make up X-radiation, a form of electromagnetic radiation.
The 19th century was a century that began on January 1, 1801, and ended on December 31, 1900.
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