Photoelectric effect

Introduction and historical early When a surface is exposed to electromagnetic radiation at a frequency above a certain threshold typically visible light alkali metals near ultraviolet and extreme ultraviolet metals to metals no radiation is absorbed and electrons are broadcast in 1902 Philipp Eduard Anton von Lenard observed that the energy of individual emitted electrons increased with the frequency that is related to the color of light This seems to contradict the theory of James Clerk Maxwell s light wave was thought to predict that the electron energy would be proportional to the intensity of radiation in 1905 Albert Einstein resolved this apparent paradox by describing light as composed of discrete quanta called photons now instead of continuous waves based on the theory of Max Planck s black body radiation Einstein theorized that the energy of each quantum of light was equal to the frequency multiplied by a constant of Planck s constant later called a photon above a threshold frequency has the energy to eject an electron to create the observed effect This discovery led to the revolution of quantum physics and Einstein won the Nobel Prize for Physics in 1921 Modern view has been shown that it is necessary for the quantized light to explain the photoelectric effect The most common method used by physicists to calculate the probability of an atom to eject an electron is based on the Fermi golden rule s Although based on the method of quantum mechanics to the incident light is an electromagnetic wave which makes an atom and its electrons constituents of the transition from one energy eigenstate to another state, however, the idea that the photoelectric effect demonstrates the particle nature of light persists in the event that many introductory textbooks needed While you can use the theory classical electromagnetic light to describe the effect can also be used modern quantum theory of light to describe the photoelectric effect, however, modern quantum theory of light is a particle model, since it does not always predict the results would expect for a particle interpretation ship An example is the dependence of polarization with respect to the direction of the electron emits a phenomenon that has been found useful in collecting data of polarization of black holes and stars Traditional explanation neutron a photon beam of light energy having a characteristic determined by the frequency of light in the process if an electron photoemission in any material absorbs a photon energy and therefore has more energy than the function of work of the electron energy of binding of material is ejected if the photon energy is too low, the electron is unable to escape from the material increase in the intensity of the light beam increases the number of photons in the beam and therefore increases the number of electrons emitted, but does not increase the energy that each electron has Thus the energy of the electrons emitted depends not the intensity of incoming light, but only to the energy of individual photons This is true provided that when the intensity is low enough for nonlinear effects caused by multiphoton absorption or level moves such as AC Stark effect to be negligible This was a proposal at the time of Einstein, long before lasers were invented citation needed electrons can absorb energy from photons when irradiated, but usually follow a principle of all or nothing All of the energy of a photon must be absorbed and used to free an electron from atomic binding energy or re issued if the photon energy is absorbed some of the energy release the electron from the atom and the rest contributes to the kinetic energy of the electron s as a free particle citation needed experimental results of the photoelectric emission for a given metal and frequency of incident radiation, the speed at which ejected photoelectrons is directly proportional to the intensity of incident light for a given metal there is a certain minimum frequency of the incident radiation below which can not be emitted photoelectrons This frequency is called frequency threshold for a particular given metal of work function increase in the frequency of the incident beam intensity increases the photoelectric current Above the threshold frequency of the maximum kinetic energy of the photoelectron emitted depends on the frequency of the incident light, but is independent the intensity of incident light, provided that the latter is not too high the time between the incidence of radiation and a photoelectron emission is very little less than 109 seconds The distribution of the direction of electrons emitted peaks the polarization direction of the electric field direction of the incident light is linearly polarized if citation needed mathematical description The maximum kinetic energy Kmax an ejected electron is given by where h is Planck's constant f is the frequency of the incident photon and HF0 job function is sometimes denoted W which is the minimum energy required to remove an electron delocalized on the surface of any metal can be given work function, in turn written as where f 0 is called the threshold frequency for the metal's maximum kinetic energy of an electron ejected is because the kinetic energy of the electron must be positive follows that the frequency f of the incident photon must be greater than f 0 so that the photoelectric effect occurring Model of three steps in the scheme X-ray photoelectric effect in the crystalline material is often divided into three steps photoelectric effect see below photodiode inside the hole left behind can result in a spiral effect which is visible even when the electron not leave the material in very molecular solids phonons happy in this step and may be visible as lines of energy of the electrons at the end of the internal photoelectric effect must be allowed dipole transition rules to translate the atoms through the tight-binding model on the glass and are similar in geometry of the oscillations in plasma which must be transverse transport medium ballistic electrons to the surface leakage Some electrons are scattered electrons from the material in the surface model in three steps which an electron can take various routes through of these three steps All roads may interfere with the direction of the path integral formulation for the surface states and the molecules of a three-step model follows that in some sense, as even most atoms have multiple electrons dispersion that can electron leaving the necessary appointments Early observations of History In 1839 Alexandre Edmond Becquerel observed the photoelectric effect by means of an electrode in a conductive solution exposed to light at 1873 Willoughby Smith found that selenium photoconductive citation is needed s spark gaps Hertz Heinrich Hertz in 1887 observed the photoelectric effect and the production and reception of electromagnetic waves, these observations published in the journal Annalen der Physik The receiver consisted of a coil with a spark gap, where you see a spark in the detection of electromagnetic waves put the apparatus in a dark box to see better spark however noted that the maximum length is reduced when spark in the box a glass panel positioned between the electromagnetic wave source and receiver which absorbs ultraviolet radiation helped the electrons jump across the gap When removing the spark length would increase He observed no decrease in spark length when replacing the quartz glass and quartz does not absorb UV radiation Hertz concluded his months of research and reported the results He continue with the investigation of this effect nor made any attempt to explain how this phenomenon was due to the citation needed Stoletov the first law of the photoelectric effect in the period between February 1888 and until 1891 a detailed analysis of the photoelectric effect was made by Aleksandr Stoletov with the results published in 6 works by four of them in Comptes Rendus a review translated from Russian Physikalische Revue and the last piece in the Journal of Physics first devised these works Stoletov a new experimental setup, which was more suitable for quantitative analysis of PhotoEffect With this setup was found direct proportionality between the intensity of light and the induced electric current photo of the first law of the photoelectric effect or the law Stoletov s One of his Other findings as a result of measurement of the dependence of the intensity of electric current picture in the gas pressure, which found the existence of a gas pressure Pm corresponding to an optimum maximum photocurrent this property is used for the creation of solar cells citation needed In 1899 JJ Thomson JJ Thomson electrons investigated ultraviolet light in Crookes tubes influenced by the work of James Clerk Maxwell, Thomson deduced that cathode rays consisted of negatively charged particles called electrons later that he called corpuscles in the investigation of Thomson enclosed a metal plate of a cathode in a vacuum tube and exposed to high frequency radiation fields was thought that oscillating electromagnetic field caused the atoms to resonate and after reaching a certain amplitude caused a corpuscle subatomic to be emitted and the current to be detected amount of this current varies with the intensity and color of the radiation intensity of the radiation frequency larger or more necessary current quotation produce radiant energy ray photoelectric motor driver included in the isolated a capacitor connected to the capacitor is electrically charged Tesla described the photoelectric effect in 1901 described radiation as vibrations of the ether of small wavelengths the atmosphere ionized The November 5, 1901 received a patent US685957 Apparatus for the Utilization of Energy describes radiation radiant loading and unloading conductors This was done by using a metal plate or a piece of mica exposed to radiant energy used Tesla this effect to charge a capacitor with energy by means of a conductive plate precursor by a the solar radiant energy is removed with high speed small particles ie, electrons are strongly electrified The patent specifies that the radiation or radiant energy including many different ways these devices are referred to as AC photoelectric citation needed stepper motors in practice a polished metal plate isolated or body of another embodiment of the sunlight radiant energy such as obtain a positively charged electrons are emitted by the plate As the positively charged plate electrons form an electrostatic force in the board due to emissions from the surface of the photoelectrons and drain the negatively charged capacitors in Tesla patent application noted that as the rays or radiation falling on the insulated wire that is connected to a capacitor electrically charged capacitor indefinitely Von Lenard's observations s In 1902 Philipp Lenard observed the variation of electron energy with light frequency He used a powerful electric arc lamp allowed to investigate the major changes in the intensity and had sufficient power to enable it investigate the variation of potential with the frequency of light experiment directly measured potentials kinetic energy of electrons found the electron energy by relating it to a high voltage potential stop in a phototube was found that the calculated maximum electron kinetic energy is determined by the frequency of light, for example an increase in frequency results in an increase in the maximum kinetic energy calculated for an electron to release ultraviolet radiation would require a higher potential applied to stop the flow stop in a light phototube However blue Lenard s results were more qualitative than quantitative due to the difficulty of performing the experiments, the experiments must be done in the freshly cut metal so that the pure metal, but rust was observed in minutes, even in partial gaps use the current emitted by the surface was determined by light intensity or brightness s double the light intensity doubled the number of electrons emitted from the surface Lenard did not know of the appointment photons necessary mathematical description of Einstein Albert Einstein , the light quanta s in 1905 of how the photoelectric effect was caused by the absorption of quanta of photons of light that is now called in the newspaper called the heuristic point of view on the production and transformation of light this work proposed the simple description of light quanta or photons and showed how to explain phenomena as the photoelectric effect The simple explanation in terms of absorption of discrete quanta of light explained the features of the phenomenon and the explanation of Einstein frequency characteristic s the photoelectric effect won him the Nobel Prize for Physics in 1921 The idea of ​​light quanta began with Max Planck's published law s of black body radiation in the law of energy distribution in the normal spectrum Annalen der Physik April 1901 , assuming that Hertzian oscillators could only exist at energies E proportional to the frequency f of the oscillator by E hf where h is Planck's constant s By assuming that light actually consisted of discrete packets of energy in Einstein wrote an equation for the photoelectric effect the experiments installed explains why energy photoelectrons were only dependent on the frequency of the incident light intensity and not a source of high frequency low intensity could provide a few high energy photons, while a source of high intensity low frequency could supply any individual photons sufficient energy to dislodge electrons This was a great theoretical leap, but the concept was strongly resisted at first b
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