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Quantum electrodynamics

Quantum electrodynamics
In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction. History[edit] The first formulation of a quantum theory describing radiation and matter interaction is attributed to British scientist Paul Dirac, who (during the 1920s) was first able to compute the coefficient of spontaneous emission of an atom.[2] Difficulties with the theory increased through the end of 1940. QED has served as the model and template for all subsequent quantum field theories. Feynman's view of quantum electrodynamics[edit] Introduction[edit] or Related:  QUANTUM PHYSICSLeseliste

Photoelectric effect The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner may be called photoelectrons. According to classical electromagnetic theory, this effect can be attributed to the transfer of energy from the light to an electron in the metal. From this perspective, an alteration in either the amplitude or wavelength of light would induce changes in the rate of emission of electrons from the metal. Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency, below which no electrons can be emitted from the metal regardless of the amplitude and temporal length of exposure of light. In 1887, Heinrich Hertz[2][3] discovered that electrodes illuminated with ultraviolet light create electric sparks more easily. The photoelectric effect requires photons with energies from a few electronvolts to over 1 MeV in elements with a high atomic number. where

The most ridiculous job interview questions As if job interviews weren't stressful enough, hiring managers at some of the largest companies have taken to throwing real curve balls. Here's a sampling of the wackiest questions. By Anne Fisher, contributor FORTUNE -- With about five candidates for every job opening these days, some responsible for hiring decisions have resorted to desperate measures in their efforts to narrow the field. Glassdoor.com culled through tens of thousands of queries reported by job seekers who had done their best to come up with answers on the spot, and selected the oddest interview questions of the past 15 months. Luckily for beleaguered candidates, the interviewers seemed in most cases to be more interested in how people responded -- that is, in hearing their thought process, and seeing how well they kept their cool -- than in receiving a "correct" response. "Using a scale of 1 to 10, rate yourself on how weird you are." -- Capital One (COF) "How many balloons would fit in this room?" Also on Fortune.com:

Quantum hydrodynamics Quantum hydrodynamics (QHD) is most generally the study of hydrodynamic systems which demonstrate behavior implicit in quantum subsystems (usually quantum tunnelling). They arise in semiclassical mechanics in the study of semiconductor devices, in which case being derived from the Wigner–Boltzmann equation. In quantum chemistry they arise as solutions to chemical kinetic systems, in which case they are derived from the Schrödinger equation by way of Madelung equations. An important system of study in quantum hydrodynamics is that of superfluidity. Some other topics of interest in quantum hydrodynamics are quantum turbulence, quantized vortices, second and third sound, and quantum solvents. Some common experimental applications of these studies are in liquid helium (He-3 and He-4), and of the interior of neutron stars and the quark–gluon plasma.

First quantization 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. First quantization is appropriate for studying a single quantum-mechanical system being controlled by a laboratory apparatus that is itself large enough that classical mechanics is applicable to most of the apparatus. Theoretical background[edit] The starting point is the notion of quantum states and the observables of the system under consideration. Quantum theory postulates that all quantum states are represented by state vectors in a Hilbert space, and that all observables are represented by Hermitian operators acting on that space.[1] Parallel state vectors represent the same physical state, and therefore one mostly deals with normalized state vectors. , i. e and . as . . . .

Vector From Wikipedia, the free encyclopedia Vector may refer to: In mathematics and physics[edit] In computer science[edit] In biology[edit] In business[edit] In entertainment[edit] Fictional characters and elements[edit] Other uses[edit] See also[edit] Quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is a theory of strong interactions, a fundamental force describing the interactions between quarks and gluons which make up hadrons such as the proton, neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory with symmetry group SU(3). The QCD analog of electric charge is a property called 'color'. Gluons are the force carrier of the theory, like photons are for the electromagnetic force quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. QCD enjoys two peculiar properties: Confinement, which means that the force between quarks does not diminish as they are separated. There is no known phase-transition line separating these two properties; confinement is dominant in low-energy scales but, as energy increases, asymptotic freedom becomes dominant. Terminology[edit] History[edit] Three identical quarks cannot form an antisymmetric S-state. Theory[edit]

Facing awkward job interview questions Some potential employers knowingly ask candidates bizarre questions too see how they react. Certain topics interviewer cannot broach, but awkward questions may still be askedYou can always toss an awkward question back at the interviewerYou can also ignore the question by acknowledging it and quickly moving onto another subjectRemember that an interview is a two-way street. You're also deciding if you want them (CNN) -- With the economy picking up and college graduation season upon us, job interviews are on the rise. Those of you making the interview rounds may not realize that the law bars prospective employers from asking certain questions. Before former Oklahoma State wide receiver Dez Bryant was drafted into the NFL last month to play for the Dallas Cowboys he was asked one such inappropriate question. Ireland later apologized. Bryant had stated during the pre-draft interview that his father was a pimp and that his mother worked for him.

Pauli exclusion principle A more rigorous statement is that the total wave function for two identical fermions is anti-symmetric with respect to exchange of the particles. This means that the wave function changes its sign if the space and spin co-ordinates of any two particles are interchanged. Integer spin particles, bosons, are not subject to the Pauli exclusion principle: any number of identical bosons can occupy the same quantum state, as with, for instance, photons produced by a laser and Bose–Einstein condensate. Overview[edit] "Half-integer spin" means that the intrinsic angular momentum value of fermions is (reduced Planck's constant) times a half-integer (1/2, 3/2, 5/2, etc.). History[edit] In the early 20th century it became evident that atoms and molecules with even numbers of electrons are more chemically stable than those with odd numbers of electrons. Pauli looked for an explanation for these numbers, which were at first only empirical. Connection to quantum state symmetry[edit] and the other in state

Single and many-particle Quantum mechanics Electric field Electric field lines emanating from a point positive electric charge suspended over an infinite sheet of conducting material. Qualitative description[edit] An electric field that changes with time, such as due to the motion of charged particles producing the field, influences the local magnetic field. That is: the electric and magnetic fields are not separate phenomena; what one observer perceives as an electric field, another observer in a different frame of reference perceives as a mixture of electric and magnetic fields. For this reason, one speaks of "electromagnetism" or "electromagnetic fields". In quantum electrodynamics, disturbances in the electromagnetic fields are called photons. Definition[edit] Electric Field[edit] Consider a point charge q with position (x,y,z). Notice that the magnitude of the electric field has dimensions of Force/Charge. Superposition[edit] Array of discrete point charges[edit] Electric fields satisfy the superposition principle. Continuum of charges[edit]

Quantum Diaries We’ve been discussing the Higgs (its interactions, its role in particle mass, and its vacuum expectation value) as part of our ongoing series on understanding the Standard Model with Feynman diagrams. Now I’d like to take a post to discuss a very subtle feature of the Standard Model: its chiral structure and the meaning of “mass.” This post is a little bit different in character from the others, but it goes over some very subtle features of particle physics and I would really like to explain them carefully because they’re important for understanding the entire scaffolding of the Standard Model. My goal is to explain the sense in which the Standard Model is “chiral” and what that means. Helicity Fact: every matter particle (electrons, quarks, etc.) is spinning, i.e. each matter particle carries some intrinsic angular momentum. Let me make the caveat that this spin is an inherently quantum mechanical property of fundamental particles! This is our spinning particle. Sounds good? Chirality

Ace the odd interview questions No matter how odd the question, answer in a way that reflects best on your personality. Hiring managers veer from traditional interview questions to pick up on personality traitscompanies want people who can help the business prosper in a tough economic environmentNo matter the question, what you say should be tied to your qualifications for the position (CareerBuilder.com) -- Turns out that job seekers are not the only ones getting creative in the interview process. A new CareerBuilder survey of hiring managers revealed that they, too, are starting to veer from the traditional interview questions in order to get candidates to offer up even more unique glimpses into their personality. According to the latest Job Openings and Labor Turnover Survey (JOLTS) conducted by the Bureau of Labor Statistics, the number of applicants competing for every job opening in the U.S. is double the historic norm at seven candidates per opening. Q: Do you believe in UFOS? Let's be honest -- everyone has.

Axiomatic approaches Lagrangian formalism

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