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115-401: An image dissector focuses a visual image onto a layer of photosensitive material, such as cesium oxide , which emits negatively charged "photoelectrons" proportional to the intensity of the light striking the material. Electrostatic deflecting plates or magnetic fields then periodically manipulate the resulting electron image horizontally and vertically before an electron multiplier , or

230-622: A $ 10 million gift from Athena and Nicholas Karabots towards the Inspire Science! capital campaign. This gift is the largest gift in the institute's history, and put the Franklin Institute within $ 6 million of the $ 64.7 million capital campaign goal. The Nicholas and Athena Karabots Pavilion will house not only a $ 10 million multiroom exhibit on neuroscience, but also a conference center, classroom space, and additional room for traveling exhibitions. The most recognizable part of

345-462: A Heuristic Viewpoint Concerning the Production and Transformation of Light". The paper proposed a simple description of energy quanta , and showed how they explained the blackbody radiation spectrum. His explanation in terms of absorption of discrete quanta of light agreed with experimental results. It explained why the energy of photoelectrons was not dependent on incident light intensity . This

460-407: A combination of both methods is used. Additional kinetic energy is required to move an electron out of the conduction band and into the vacuum level. This is known as the electron affinity of the photocathode and is another barrier to photoemission other than the forbidden band, explained by the band gap model. Some materials such as gallium arsenide have an effective electron affinity that is below

575-462: A crude approximation, for photon energies above the highest atomic binding energy, the cross section is given by: Here Z is the atomic number and n is a number which varies between 4 and 5. The photoelectric effect rapidly decreases in significance in the gamma-ray region of the spectrum, with increasing photon energy. It is also more likely from elements with high atomic number. Consequently, high- Z materials make good gamma-ray shields, which

690-407: A detailed analysis of the photoeffect was performed by Aleksandr Stoletov with results reported in six publications. Stoletov invented a new experimental setup which was more suitable for a quantitative analysis of the photoeffect. He discovered a direct proportionality between the intensity of light and the induced photoelectric current (the first law of photoeffect or Stoletov's law ). He measured

805-421: A fully electronic television system. In 1929 Farnsworth eliminated a motor generator from the system, so it then had no mechanical parts. Further developments that year included improvements in image clarity and an increase in the number of lines of resolution, such that it exceeded that of the mechanical television systems. Also in 1929, Farnsworth transmitted the first live human images with his system, including

920-430: A laser, a discharge tube, or a synchrotron radiation source. The concentric hemispherical analyzer is a typical electron energy analyzer. It uses an electric field between two hemispheres to change (disperse) the trajectories of incident electrons depending on their kinetic energies. Photons hitting a thin film of alkali metal or semiconductor material such as gallium arsenide in an image intensifier tube cause

1035-439: A moving visual image. The early electronic camera tubes (like the image dissector ) suffered from a very disappointing fatal flaw: They scanned the subject and what was seen at each point was only the tiny piece of light viewed at the instant that the scanning system passed over it. Because the dissector does not store charge, it is useful for viewing the inside of furnaces and monitoring welding systems as it does not suffer from

1150-405: A powerful electric arc lamp which enabled him to investigate large changes in intensity. However, Lenard's results were qualitative rather than quantitative because of the difficulty in performing the experiments: the experiments needed to be done on freshly cut metal so that the pure metal was observed, but it oxidized in a matter of minutes even in the partial vacuums he used. The current emitted by

1265-406: A screen charged by the photoelectric effect to transform an optical image into a scanned electronic signal. Because the kinetic energy of the emitted electrons is exactly the energy of the incident photon minus the energy of the electron's binding within an atom, molecule or solid, the binding energy can be determined by shining a monochromatic X-ray or UV light of a known energy and measuring

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1380-442: A series of electrodes (dynodes) at ever-higher potentials, these electrons are accelerated and substantially increased in number through secondary emission to provide a readily detectable output current. Photomultipliers are still commonly used wherever low levels of light must be detected. Video camera tubes in the early days of television used the photoelectric effect. For example, Philo Farnsworth 's " Image dissector " used

1495-403: A small aperture leading to a positively charged detector, or just an anode , in the case of the earliest dissector tubes. The electron multiplier or aperture permits only those electrons emanating from a very small area of the electron image, representing a similarly small area of the visual image. The entire image is scanned several times per second to produce an electrical signal that represented

1610-499: A strong relationship between light and electronic properties of materials. In 1873, Willoughby Smith discovered photoconductivity in selenium while testing the metal for its high resistance properties in conjunction with his work involving submarine telegraph cables. Johann Elster (1854–1920) and Hans Geitel (1855–1923), students in Heidelberg , investigated the effects produced by light on electrified bodies and developed

1725-433: A three and a half-inch image of his wife Elma ("Pem") with her eyes closed (possibly due to the bright lighting required). Since the electrons emitted within an image dissector are collected by the electron multiplier or anode only during the very brief time an area of the "electron image" is exposed, the bulk of the electrons are lost. Thus the earliest image dissectors were very inefficient, and extremely bright illumination

1840-539: A view further to develop the resources of the union, increase the national independence, call forth the ingenuity and industry of the people, and thereby increase the comforts of the community at large. Begun in 1825, the institute was an important force in the professionalization of American science and technology through the nineteenth century, beginning with early investigations into steam engines and water power . In addition to conducting scientific inquiry, it fostered research and education by running schools, publishing

1955-612: Is featured in Benjamin Franklin Forever , an hourly 3.5-minute multimedia presentation utilizing the entire rotunda. Also noteworthy is the Franklin Institute's Frankliniana Collection, some of which is on rotating display in the Pendulum Staircase. Highlights include Franklin's 1777 Nini Medallion, the scale model of the bust from the statue in the Memorial, the figurehead of Franklin's bust from

2070-974: Is a member of the Association of Science and Technology Centers (ASTC) and the American Alliance of Museums (AAM). The Franklin Institute is also a member of the Science Museum Exhibit Collaborative with the Fort Worth Museum of Science & History; the Museum of Science, Boston ; COSI Columbus , formerly known as the Center of Science and Industry in Columbus, Ohio ; OMSI in Portland, Oregon ;

2185-427: Is an IMAX dome theater that is 180° encompassing and tilted at 30 degrees. The seating places the audience up in the dome which is over 70 ft (21 m) across and 4.5 stories tall. In addition, the theater has 20,000 watts of amplifier power and over 50 speakers. The theater was closed in 2020 due to COVID-19 , and did not reopen with the rest of the museum. In November 2023, the Franklin Institute confirmed that

2300-419: Is one of the main characteristics of the quantum system, and can be used for further studies in quantum chemistry and quantum physics. The electronic properties of ordered, crystalline solids are determined by the distribution of the electronic states with respect to energy and momentum—the electronic band structure of the solid. Theoretical models of photoemission from solids show that this distribution is, for

2415-416: Is positive, and ν > ν o {\displaystyle \nu >\nu _{o}} is required for the photoelectric effect to occur. The frequency ν o {\displaystyle \nu _{o}} is the threshold frequency for the given material. Above that frequency, the maximum kinetic energy of the photoelectrons as well as the stopping voltage in

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2530-508: Is proportional to the frequency ν {\displaystyle \nu } of the corresponding electromagnetic wave. The proportionality constant h {\displaystyle h} has become known as the Planck constant . In the range of kinetic energies of the electrons that are removed from their varying atomic bindings by the absorption of a photon of energy h ν {\displaystyle h\nu } ,

2645-416: Is sigmoidal, but its exact shape depends on the experimental geometry and the electrode material properties. For a given metal surface, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This frequency is called the threshold frequency . Increasing the frequency of the incident beam increases the maximum kinetic energy of the emitted photoelectrons, and

2760-400: Is stopped, the current also stops. This initiated the concept of photoelectric emission. The discovery of the ionization of gases by ultraviolet light was made by Philipp Lenard in 1900. As the effect was produced across several centimeters of air and yielded a greater number of positive ions than negative, it was natural to interpret the phenomenon, as J. J. Thomson did, as a Hertz effect upon

2875-761: Is the principal reason why lead ( Z  = 82) is preferred and most widely used. Applets Franklin Institute The Franklin Institute is a science museum and the center of science education and research in Philadelphia , Pennsylvania . It is named after the American scientist and statesman Benjamin Franklin . It houses the Benjamin Franklin National Memorial . Founded in 1824,

2990-471: Is thought that the smallest particles are repelled kilometers from the surface and that the particles move in "fountains" as they charge and discharge. When photon energies are as high as the electron rest energy of 511 keV , yet another process, Compton scattering , may occur. Above twice this energy, at 1.022 MeV , pair production is also more likely. Compton scattering and pair production are examples of two other competing mechanisms. Even if

3105-407: Is too low, the electron is unable to escape the material. Since an increase in the intensity of low-frequency light will only increase the number of low-energy photons, this change in intensity will not create any single photon with enough energy to dislodge an electron. Moreover, the energy of the emitted electrons will not depend on the intensity of the incoming light of a given frequency, but only on

3220-426: Is very small, less than 10 second. Angular distribution of the photoelectrons is highly dependent on polarization (the direction of the electric field) of the incident light, as well as the emitting material's quantum properties such as atomic and molecular orbital symmetries and the electronic band structure of crystalline solids. In materials without macroscopic order, the distribution of electrons tends to peak in

3335-426: The "Kite and Key" experiment . In 1826, The Journal of The Franklin Institute was established to publish US Patent information and to document scientific and technological achievements throughout the nation. It is the second oldest continuously published scientific journal in the country, and is now primarily devoted to engineering and applied mathematics . Since 1824, the Franklin Institute has maintained

3450-496: The Fermi level . When the photoelectron is emitted into a solid rather than into a vacuum, the term internal photoemission is often used, and emission into a vacuum is distinguished as external photoemission . Even though photoemission can occur from any material, it is most readily observed from metals and other conductors. This is because the process produces a charge imbalance which, if not neutralized by current flow, results in

3565-727: The Franklin Institute in Philadelphia, Pennsylvania . In April 1933, Farnsworth submitted a patent application entitled Image Dissector , but which actually detailed a charge storage low electron velocity cathode ray tube (CRT) camera tube. Its principles were developed and implemented by RCA. Though RCA had paid royalties though in 1939, legal cost associated with RCA's patent dispute, war time manufacturing pressure, Farnsworths patent expiring just eight years later, and his understandable disillusionment his company would be dissolved shortly after world war two. The image dissector with its many pitfalls would rapidly be replaced through

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3680-679: The Pantheon in Rome . The Hall is 82 ft (25 m) in length, width, and height. The domed ceiling is self-supporting and weighs 1600 tons. The floors, walls, columns, pilasters, and cornices are made of marbles imported from Portugal, Italy, and France. The United States Congress designated the Hall and statue as the official Benjamin Franklin National Memorial on October 25, 1972 ( Pub. L.   92–551 ). The Memorial

3795-732: The Science Museum of Minnesota in Saint Paul, Minnesota ; and the California Science Center , formerly the California Museum of Science & Industry, in Los Angeles . The Benjamin Franklin National Memorial features a 20-foot (6.1 m) high marble statue, sculpted by James Earle Fraser . Originally opened in 1938, the Memorial was designed by architect John T. Windrim and modeled after

3910-708: The University of Delaware and named Bartol Research Institute . The Franklin Institute Laboratories for Research and Development operated from the Second World War into the 1980s. Many scientists have demonstrated groundbreaking new technology at the Franklin Institute. From September 2 to October 11, 1884, it hosted the International Electrical Exhibition of 1884 , the first great electrical exposition in

4025-624: The frigate USS  Franklin , his ceremonial sword used in the court of King Louis XVI, and the odometer that Franklin used to measure the postal routes in Philadelphia. Additionally, the institute's Electricity exhibition highlights one of Franklin's lightning rods, his electricity tube, a Franklin Electrostatic Generator , the 1751 publication of Franklin's Experiments and Observations on Electricity , and Thornton Oakley 's two 1940 historical murals of Franklin and

4140-411: The kinetic energy of the emitted electrons, with sufficiently dim light resulting in a delayed emission. The experimental results instead show that electrons are dislodged only when the light exceeds a certain frequency —regardless of the light's intensity or duration of exposure. Because a low-frequency beam at a high intensity does not build up the energy required to produce photoelectrons, as would be

4255-402: The photovoltaic effect , and the photoelectrochemical effect . The photons of a light beam have a characteristic energy, called photon energy , which is proportional to the frequency of the light. In the photoemission process, when an electron within some material absorbs the energy of a photon and acquires more energy than its binding energy , it is likely to be ejected. If the photon energy

4370-523: The "flare" normal picture tubes experience when looking at intense lights. In April 1925, German professor Max Dieckmann and his student Rudolf Hell applied for a patent for a device named Lichtelektrische Bildzerlegerröhre für Fernseher (Photoelectric Image Dissector Tube for Television) under the German patent number: DE450187C. A patent was issued in October 1927, and their experiments were announced in

4485-413: The "world's largest drawing by an individual". In 2006, the Franklin Institute began fundraising activities for the Inspire Science! capital campaign, a $ 64.7 million campaign intended to fund the construction of a 53,000 sq ft (4,900 m ) building addition, new exhibits, and upgrades and renovations to the existing Institute building and exhibits. In 2011, the Franklin Institute received

4600-486: The 1930s by the image orthicon and iconoscopes , until the 1980s when they would also be replaced by solid state image sensors. Photoelectric effect The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light . Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics , solid state , and quantum chemistry to draw inferences about

4715-418: The American nationwide distributed magazines Discovery and Popular Radio , but they failed to reduce it to practice . In 1951, Hell claimed that he had made a tube but could not get it to function, since at the time there was an insufficient knowledge of electron optics , the manipulation of an electron beam by electric or magnetic fields . American television pioneer Philo T. Farnsworth invented

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4830-513: The Arts determines the winners of these awards. Recipients and related information can be found in the laureates database. The Franklin Institute also undertakes research in informal science education. Areas of special strength are educational technology, school partnerships, and youth leadership. In addition, the center has built a substantial portfolio of unique online resources of the history of science, including online exhibits on Ben Franklin and

4945-534: The Benjamin Franklin Memorial, Inc. raised $ 5 million between December 1929 and June 1930. Only two of the four wings envisioned by Windrim were built; these face the Parkway and share design elements with other cultural and civic structures around Logan Circle . On March 31, 1940, press agent William Castellini issued a press release stating that the world would end the next day. The story

5060-574: The Bower Award and Prize for Achievement in Science (Bower Science Award) and the Bower Award for Business Leadership have been awarded annually. They are funded by a $ 7.5 million bequest in 1988 from Henry Bower, a chemical manufacturer in Philadelphia. The Bower Science Award contains $ 250,000 of cash, one of the largest amounts for a science award in the US. The institute's Committee on Science and

5175-574: The Center is a partnership between the Franklin Institute and the Girl Scouts of the USA provided girls and their families a chance to learn about science together. Over 100 sites participated in the program, with over 70 of the sites still active today. Girls at the Center provided activities for the girls to do with their families at home, as well as projects to be completed on site, all culminating in

5290-886: The Edward Longstreth Medal (1890), the Howard N. Potts Medal (1911), the Franklin Medal (1915), the George R. Henderson Medal (1924), the Louis E. Levy Medal (1924), the John Price Wetherill Medal (1926), The Frank P. Brown Medal (first awarded in 1941), Stuart Ballantine Medal (1947), and the Albert A. Michelson Medal (1968). Past winners include Henry Ford , Frank Lloyd Wright , Marie Curie , and Thomas Edison . In 1998 all of

5405-427: The Franklin Institute assured people it had made no such prediction. Castellini was dismissed shortly thereafter. On December 21, 2017, during a party hosted by the museum, a partygoer with his companions slipped into a closed-off exhibit of ten terracotta warriors on loan from China . After his companions left, the partygoer broke off and stole a thumb from one of the warriors. Law enforcement agents later recovered

5520-692: The Franklin Institute is one of the oldest centers of science education and development in the United States. Its chief astronomer is Derrick Pitts . On February 5, 1824, Samuel Vaughan Merrick and William H. Keating founded the Franklin Institute of the State of Pennsylvania for the Promotion of the Mechanic Arts . The opening was chronicled by The Literary Chronicle for the Year 1824 : With

5635-846: The Franklin Institute's Science Center is the Franklin Institute Science Museum . In the spirit of inquiry and discovery embodied by Benjamin Franklin, the mission of the Franklin Institute Science Museum serves to inspire an understanding of and passion for science and technology learning. Among other exhibits, the Science Museum holds the largest collection of artifacts from the Wright brothers ' workshop. The Science Center includes many pertinent attractions that are not museum exhibits. The Budd BB-1 Pioneer flying boat, in front of

5750-540: The German physicist Max Planck suggested in his "On the Law of Distribution of Energy in the Normal Spectrum" paper that the energy carried by electromagnetic waves could only be released in packets of energy. In 1905, Albert Einstein published a paper advancing the hypothesis that light energy is carried in discrete quantized packets to explain experimental data from the photoelectric effect. Einstein theorized that

5865-833: The Heart, as well as resources on the Wright Aeronautical Engineering Collection. The Franklin Institute is a member of the Nanoscale Informal Science Education Network (NISE Net). Opening in September 2006, The Science Leadership Academy is a partnership between the Franklin Institute and the School District of Philadelphia . The Franklin Institute offers summer institutes and school year mini-courses for K-8 teachers, in collaboration with

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5980-690: The School District of Philadelphia and Curriculum & Instruction Office. Partnerships for Achieving Careers in Technology and Science , or PACTS, is a year-round program of science enrichment, career development, and leadership opportunities for diverse middle- and high-school students in the Philadelphia Region. PACTS students use hands-on science workshops, field based research, field trips, and laboratory experiments to learn how science affects their everyday lives. Girls at

6095-441: The United States. The world's first public demonstration of an all-electronic television system was later given by Philo Taylor Farnsworth on August 25, 1934. The first female member, Elizabeth Skinner, was elected to membership in 1833. The Franklin Institute was integrated in 1870, when Philadelphia teacher and activist Octavius Catto was admitted as a member. The institute's original building at 15 South 7th Street, later

6210-411: The apparatus in a darkened box to see the spark better. However, he noticed that the maximum spark length was reduced when inside the box. A glass panel placed between the source of electromagnetic waves and the receiver absorbed ultraviolet radiation that assisted the electrons in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he replaced

6325-567: The case if light's energy accumulated over time from a continuous wave, Albert Einstein proposed that a beam of light is not a wave propagating through space, but a swarm of discrete energy packets, known as photons —term coined by Gilbert N. Lewis in 1926. Emission of conduction electrons from typical metals requires a few electron-volt (eV) light quanta, corresponding to short-wavelength visible or ultraviolet light. In extreme cases, emissions are induced with photons approaching zero energy, like in systems with negative electron affinity and

6440-511: The defendant was being "overcharged" under statutes applicable to professional art thieves. An April 2019 trial ended in a hung jury with seven of the 12 jurors in favor of acquittal. A February 2020 retrial was postponed due to travel restrictions related to the COVID-19 pandemic . In 2021, the institute housed the work of Dyymond Whipper-Young as she broke the Guinness world record for

6555-567: The dependence of the intensity of the photo electric current on the gas pressure, where he found the existence of an optimal gas pressure corresponding to a maximum photocurrent ; this property was used for the creation of solar cells . Many substances besides metals discharge negative electricity under the action of ultraviolet light. G. C. Schmidt and O. Knoblauch compiled a list of these substances. In 1897, J. J. Thomson investigated ultraviolet light in Crookes tubes . Thomson deduced that

6670-467: The device, which would come to be called a " multipactor ", such that it reportedly could amplify a signal to the 60th power or better, and showed great promise in other fields of electronics. A significant problem with the multipactor, however, was that it wore out at an unsatisfactorily rapid rate. On August 25, 1934, Farnsworth gave the world's first public demonstration of a complete, all-electronic television system, which included his image dissector, at

6785-467: The direction of polarization of linearly polarized light. The experimental technique that can measure these distributions to infer the material's properties is angle-resolved photoemission spectroscopy . In 1905, Einstein proposed a theory of the photoelectric effect using a concept that light consists of tiny packets of energy known as photons or light quanta. Each packet carries energy h ν {\displaystyle h\nu } that

6900-498: The ejected particles, which he called corpuscles, were of the same nature as cathode rays . These particles later became known as the electrons. Thomson enclosed a metal plate (a cathode) in a vacuum tube, and exposed it to high-frequency radiation. It was thought that the oscillating electromagnetic fields caused the atoms' field to resonate and, after reaching a certain amplitude, caused subatomic corpuscles to be emitted, and current to be detected. The amount of this current varied with

7015-408: The ejection of photoelectrons due to the photoelectric effect. These are accelerated by an electrostatic field where they strike a phosphor coated screen, converting the electrons back into photons. Intensification of the signal is achieved either through acceleration of the electrons or by increasing the number of electrons through secondary emissions, such as with a micro-channel plate . Sometimes

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7130-478: The electron's binding energy. The distribution of kinetic energies thus reflects the distribution of the binding energies of the electrons in the atomic, molecular or crystalline system: an electron emitted from the state at binding energy E B {\displaystyle E_{B}} is found at kinetic energy E k = h ν − E B {\displaystyle E_{k}=h\nu -E_{B}} . This distribution

7245-439: The electrons would 'gather up' energy over a period of time, and then be emitted. These are extremely light-sensitive vacuum tubes with a coated photocathode inside the envelope. The photo cathode contains combinations of materials such as cesium, rubidium, and antimony specially selected to provide a low work function, so when illuminated even by very low levels of light, the photocathode readily releases electrons. By means of

7360-449: The electrons. Modern instruments for angle-resolved photoemission spectroscopy are capable of measuring these quantities with a precision better than 1 meV and 0.1°. Photoelectron spectroscopy measurements are usually performed in a high-vacuum environment, because the electrons would be scattered by gas molecules if they were present. However, some companies are now selling products that allow photoemission in air. The light source can be

7475-423: The emission from excited states, or a few hundred keV photons for core electrons in elements with a high atomic number . Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality . Other phenomena where light affects the movement of electric charges include the photoconductive effect,

7590-577: The endowed medals were reorganized as the Benjamin Franklin Medals . Multiple medals are given every year, for different fields of science and engineering. The fields awarded today are " Chemistry ", " Computer and Cognitive Science ", " Earth and Environmental Science ", " Electrical Engineering ", " Life Science ", " Mechanical Engineering " and " Physics ". In the past also the fields " Earth Science ", " Engineering " and " Materials Science " were rewarded. Additionally since 1990,

7705-453: The energy in each quantum of light was equal to the frequency of light multiplied by a constant, later called the Planck constant . A photon above a threshold frequency has the required energy to eject a single electron, creating the observed effect. This was a step in the development of quantum mechanics . In 1914, Robert A. Millikan 's highly accurate measurements of the Planck constant from

7820-462: The energy of the individual photons. While free electrons can absorb any energy when irradiated as long as this is followed by an immediate re-emission, like in the Compton effect , in quantum systems all of the energy from one photon is absorbed—if the process is allowed by quantum mechanics —or none at all. Part of the acquired energy is used to liberate the electron from its atomic binding, and

7935-593: The exhibit left Philadelphia on September 30, 2007, it traveled to London . This exhibit was nearly twice the size of the original Tutankhamun exhibit of the 1970s, and contained 50 objects directly from Tut's tomb, as well as nearly 70 object from the tombs of his ancestors in The Valley of the Kings . The show also featured a CAT Scan that revealed what the Boy King may have looked like. The Franklin Institute

8050-681: The exhibits in order to learn how things work." Funds to build the new Institute and Franklin Memorial came from the Poor Richard Club, the City Board of Trust, the Benjamin Franklin Memorial, Inc., and the Franklin Institute. John T. Windrim's original design was a completely square building surrounding the Benjamin Franklin Statue, which had yet to be built. Despite the effects of the Great Depression ,

8165-417: The experiment V o = h e ( ν − ν o ) {\textstyle V_{o}={\frac {h}{e}}\left(\nu -\nu _{o}\right)} rise linearly with the frequency, and have no dependence on the number of photons and the intensity of the impinging monochromatic light. Einstein's formula, however simple, explained all the phenomenology of

8280-399: The final state of a finite crystal for which the wave function is free-electron-like outside of the crystal, but has a decaying envelope inside. In 1839, Alexandre Edmond Becquerel discovered the related photovoltaic effect while studying the effect of light on electrolytic cells . Though not equivalent to the photoelectric effect, his work on photovoltaics was instrumental in showing

8395-495: The first functional image dissector in 1927, submitting a patent application on January 7, 1927. On September 7 of that year, the image dissector successfully transmitted its first image, a simple straight line, at Farnsworth's laboratory at 202 Green Street in San Francisco . By September 3, 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press, the first such successful demonstration of

8510-452: The first practical photoelectric cells that could be used to measure the intensity of light. They arranged metals with respect to their power of discharging negative electricity: rubidium , potassium , alloy of potassium and sodium, sodium , lithium , magnesium , thallium and zinc ; for copper , platinum , lead , iron , cadmium , carbon , and mercury the effects with ordinary light were too small to be measurable. The order of

8625-426: The glass with quartz, as quartz does not absorb UV radiation. The discoveries by Hertz led to a series of investigations by Wilhelm Hallwachs , Hoor, Augusto Righi and Aleksander Stoletov on the effect of light, and especially of ultraviolet light, on charged bodies. Hallwachs connected a zinc plate to an electroscope . He allowed ultraviolet light to fall on a freshly cleaned zinc plate and observed that

8740-401: The highest kinetic energy K max {\displaystyle K_{\max }} is K max = h ν − W . {\displaystyle K_{\max }=h\,\nu -W.} Here, W {\displaystyle W} is the minimum energy required to remove an electron from the surface of the material. It is called the work function of

8855-534: The home of the (now-defunct) Atwater Kent Museum , eventually proved too small for the institute's research, educational programs, and library. The Institute moved into its current home on the Benjamin Franklin Parkway , near the intersection with 20th Street, in 1934. The new facility was intended from the start to educate visitors through hand-on interactions with exhibits: "Visitors to this museum would be encouraged to touch, handle, and operate

8970-501: The increasing potential barrier until the emission completely ceases. The energy barrier to photoemission is usually increased by nonconductive oxide layers on metal surfaces, so most practical experiments and devices based on the photoelectric effect use clean metal surfaces in evacuated tubes. Vacuum also helps observing the electrons since it prevents gases from impeding their flow between the electrodes. As sunlight, due to atmosphere's absorption, does not provide much ultraviolet light,

9085-409: The influential Journal of The Franklin Institute , sponsoring exhibitions, and recognizing scientific advancement and invention with medals and awards. In the late 20th century, the institute's research roles gave way to educating the general public through its museum. The Bartol Research Foundation of the Franklin Institute, founded in 1924 to conduct research in the physical sciences, now is part of

9200-424: The intensity and color of the radiation. Larger radiation intensity or frequency would produce more current. During the years 1886–1902, Wilhelm Hallwachs and Philipp Lenard investigated the phenomenon of photoelectric emission in detail. Lenard observed that a current flows through an evacuated glass tube enclosing two electrodes when ultraviolet radiation falls on one of them. As soon as ultraviolet radiation

9315-438: The kinetic energies of the photoelectrons. The distribution of electron energies is valuable for studying quantum properties of these systems. It can also be used to determine the elemental composition of the samples. For solids, the kinetic energy and emission angle distribution of the photoelectrons is measured for the complete determination of the electronic band structure in terms of the allowed binding energies and momenta of

9430-425: The level of the conduction band. In these materials, electrons that move to the conduction band all have sufficient energy to be emitted from the material, so the film that absorbs photons can be quite thick. These materials are known as negative electron affinity materials. The photoelectric effect will cause spacecraft exposed to sunlight to develop a positive charge. This can be a major problem, as other parts of

9545-417: The light rich in ultraviolet rays used to be obtained by burning magnesium or from an arc lamp . At the present time, mercury-vapor lamps , noble-gas discharge UV lamps and radio-frequency plasma sources, ultraviolet lasers , and synchrotron insertion device light sources prevail. The classical setup to observe the photoelectric effect includes a light source, a set of filters to monochromatize

9660-409: The light, a vacuum tube transparent to ultraviolet light, an emitting electrode (E) exposed to the light, and a collector (C) whose voltage V C can be externally controlled. A positive external voltage is used to direct the photoemitted electrons onto the collector. If the frequency and the intensity of the incident radiation are fixed, the photoelectric current I increases with an increase in

9775-419: The light. The precise relationship had not at that time been tested. By 1905 it was known that the energy of photoelectrons increases with increasing frequency of incident light and is independent of the intensity of the light. However, the manner of the increase was not experimentally determined until 1914 when Millikan showed that Einstein's prediction was correct. The photoelectric effect helped to propel

9890-550: The longest continuously awarded science and technology awards program in the United States, and one of the oldest in the world. The first issue of the Journal of The Franklin Institute , dated January 1826, makes the first written reference to these awards. Before 1998 several medals were awarded by the Franklin Institute, such as (year indicates when the award was first presented): the Elliott Cresson Medal (1875),

10005-496: The metals for this effect was the same as in Volta's series for contact-electricity, the most electropositive metals giving the largest photo-electric effect. In 1887, Heinrich Hertz observed the photoelectric effect and reported on the production and reception of electromagnetic waves. The receiver in his apparatus consisted of a coil with a spark gap , where a spark would be seen upon detection of electromagnetic waves. He placed

10120-402: The most part, preserved in the photoelectric effect. The phenomenological three-step model for ultraviolet and soft X-ray excitation decomposes the effect into these steps: There are cases where the three-step model fails to explain peculiarities of the photoelectron intensity distributions. The more elaborate one-step model treats the effect as a coherent process of photoexcitation into

10235-659: The museum, was the world's first stainless steel airplane, built by Philadelphia-based Edward F. Budd Manufacturing Corporation , and has been on display since 1935. A mock-up which would eventually become the Lunar Module in the Apollo space program, first shown on display in the 1966–67 World's Fair, held in the New York Hall of Science, is also located on the grounds. (See photo .) In 1933, Samuel Simeon Fels contributed funds to build The Fels Planetarium , only

10350-406: The particles present in the gas. In 1902, Lenard observed that the energy of individual emitted electrons was independent of the applied light intensity. This appeared to be at odds with Maxwell's wave theory of light , which predicted that the electron energy would be proportional to the intensity of the radiation. Lenard observed the variation in electron energy with light frequency using

10465-628: The past, the Science Center has hosted many traveling exhibits including Storms , Titanic , Grossology , Body Worlds , Darwin , and Robots . In the summer of 2007, the Franklin Institute hosted Tutankhamun and The Golden Age of The Pharaohs, in the Mandell Center of the Franklin Institute Science Museum. The exhibit began its United States Tour in Los Angeles , and went to Fort Lauderdale , and Chicago , before coming to Philadelphia for its final American appearance. When

10580-401: The phenomenon of photoelectric fatigue—the progressive diminution of the effect observed upon fresh metallic surfaces. According to Hallwachs, ozone played an important part in the phenomenon, and the emission was influenced by oxidation, humidity, and the degree of polishing of the surface. It was at the time unclear whether fatigue is absent in a vacuum. In the period from 1888 until 1891,

10695-422: The photoelectric effect is still commonly analyzed in terms of waves; the two approaches are equivalent because photon or wave absorption can only happen between quantized energy levels whose energy difference is that of the energy of photon. Albert Einstein's mathematical description of how the photoelectric effect was caused by absorption of quanta of light was in one of his Annus Mirabilis papers , named "On

10810-403: The photoelectric effect is the favoured reaction for a particular interaction of a single photon with a bound electron, the result is also subject to quantum statistics and is not guaranteed. The probability of the photoelectric effect occurring is measured by the cross section of the interaction, σ. This has been found to be a function of the atomic number of the target atom and photon energy. In

10925-608: The photoelectric effect supported Einstein's model, even though a corpuscular theory of light was for Millikan, at the time, "quite unthinkable". Einstein was awarded the 1921 Nobel Prize in Physics for "his discovery of the law of the photoelectric effect", and Millikan was awarded the Nobel Prize in 1923 for "his work on the elementary charge of electricity and on the photoelectric effect". In quantum perturbation theory of atoms and solids acted upon by electromagnetic radiation,

11040-465: The photoelectric effect, and had far-reaching consequences in the development of quantum mechanics . Electrons that are bound in atoms, molecules and solids each occupy distinct states of well-defined binding energies . When light quanta deliver more than this amount of energy to an individual electron, the electron may be emitted into free space with excess (kinetic) energy that is h ν {\displaystyle h\nu } higher than

11155-644: The photoelectric effect. The charged dust then repels itself and lifts off the surface of the Moon by electrostatic levitation . This manifests itself almost like an "atmosphere of dust", visible as a thin haze and blurring of distant features, and visible as a dim glow after the sun has set. This was first photographed by the Surveyor program probes in the 1960s, and most recently the Chang'e 3 rover observed dust deposition on lunar rocks as high as about 28 cm. It

11270-408: The positive voltage, as more and more electrons are directed onto the electrode. When no additional photoelectrons can be collected, the photoelectric current attains a saturation value. This current can only increase with the increase of the intensity of light. An increasing negative voltage prevents all but the highest-energy electrons from reaching the collector. When no current is observed through

11385-445: The properties of atoms, molecules and solids. The effect has found use in electronic devices specialized for light detection and precisely timed electron emission. The experimental results disagree with classical electromagnetism , which predicts that continuous light waves transfer energy to electrons, which would then be emitted when they accumulate enough energy. An alteration in the intensity of light would theoretically change

11500-407: The rate at which electrons are ejected—the photoelectric current I— but the kinetic energy of the photoelectrons and the stopping voltage remain the same. For a given metal and frequency of incident radiation, the rate at which photoelectrons are ejected is directly proportional to the intensity of the incident light. The time lag between the incidence of radiation and the emission of a photoelectron

11615-451: The rest contributes to the electron's kinetic energy as a free particle. Because electrons in a material occupy many different quantum states with different binding energies, and because they can sustain energy losses on their way out of the material, the emitted electrons will have a range of kinetic energies. The electrons from the highest occupied states will have the highest kinetic energy. In metals, those electrons will be emitted from

11730-517: The second built in the United States after Chicago 's Adler Planetarium . Fully reconstructed in 2002, the Planetarium's new design includes replacement of the original 40,000-pound stainless steel dome, originally built in 1933. The new premium dome is lighter and is 60 feet (18 m) in diameter. It is the first of its kind in the United States. The planetarium is also outfitted for visitors who are hearing impaired. The Tuttleman IMAX Theater

11845-496: The spacecraft are in shadow which will result in the spacecraft developing a negative charge from nearby plasmas. The imbalance can discharge through delicate electrical components. The static charge created by the photoelectric effect is self-limiting, because a higher charged object does not give up its electrons as easily as a lower charged object does. Light from the Sun hitting lunar dust causes it to become positively charged from

11960-556: The stolen thumb. The vandalized cavalryman is valued at US$ 4.5 million, and is considered a "priceless part of China's cultural heritage". The vandalism stoked outrage in Chinese media, such as Xinhua . The Franklin Institute blamed its external security contractor, and stated it had reviewed its security measures and procedures to prevent such situations from recurring. The defendant was charged both with theft, and with concealment of an item of cultural heritage. The defense argued that

12075-399: The stopping voltage has to increase. The number of emitted electrons may also change because the probability that each photon results in an emitted electron is a function of photon energy . An increase in the intensity of the same monochromatic light (so long as the intensity is not too high ), which is proportional to the number of photons impinging on the surface in a given time, increases

12190-571: The surface and is sometimes denoted Φ {\displaystyle \Phi } or φ {\displaystyle \varphi } . If the work function is written as W = h ν o , {\displaystyle W=h\,\nu _{o},} the formula for the maximum kinetic energy of the ejected electrons becomes K max = h ( ν − ν o ) . {\displaystyle K_{\max }=h\left(\nu -\nu _{o}\right).} Kinetic energy

12305-495: The surface was determined by the light's intensity, or brightness: doubling the intensity of the light doubled the number of electrons emitted from the surface. Initial investigation of the photoelectric effect in gasses by Lenard were followed up by J. J. Thomson and then more decisively by Frederic Palmer Jr. The gas photoemission was studied and showed very different characteristics than those at first attributed to it by Lenard. In 1900, while studying black-body radiation ,

12420-586: The theater would remain closed permanently, citing that it was financially unviable and had outdated equipment, and that the museum would be investing in other new exhibits instead. Early in 2008, extensive renovation of the museum's auditorium was completed. Previously a lecture hall, the space was renamed Franklin Theater , and features 3-D and hi-def Blu-ray digital projection capabilities. The Franklin Theater shows educational films during daytime hours while also including mass release feature-length films. In

12535-434: The then-emerging concept of wave–particle duality in the nature of light. Light simultaneously possesses the characteristics of both waves and particles, each being manifested according to the circumstances. The effect was impossible to understand in terms of the classical wave description of light, as the energy of the emitted electrons did not depend on the intensity of the incident radiation. Classical theory predicted that

12650-449: The tube, the negative voltage has reached the value that is high enough to slow down and stop the most energetic photoelectrons of kinetic energy K max . This value of the retarding voltage is called the stopping potential or cut off potential V o . Since the work done by the retarding potential in stopping the electron of charge e is eV o , the following must hold eV o  =  K max. The current-voltage curve

12765-455: The zinc plate became uncharged if initially negatively charged, positively charged if initially uncharged, and more positively charged if initially positively charged. From these observations he concluded that some negatively charged particles were emitted by the zinc plate when exposed to ultraviolet light. With regard to the Hertz effect , the researchers from the start showed the complexity of

12880-413: Was a theoretical leap, but the concept was strongly resisted at first because it contradicted the wave theory of light that followed naturally from James Clerk Maxwell 's equations of electromagnetism, and more generally, the assumption of infinite divisibility of energy in physical systems. Einstein's work predicted that the energy of individual ejected electrons increases linearly with the frequency of

12995-527: Was dedicated by Vice President Nelson Rockefeller in 1976. On December 30, 2005, Congress authorized the institute to receive up to $ 10 million in matching grants for the rehabilitation of the memorial and for the development of related exhibits. In the fall of 2008, the Benjamin Franklin National Memorial was re-opened after a summer-long restoration that included multimedia enhancements. Philadelphia's most famous citizen

13110-491: Was picked up by KYW , which reported, "Your worst fears that the world will end are confirmed by astronomers of Franklin Institute, Philadelphia. Scientists predict that the world will end at 3 p.m. Eastern Standard Time tomorrow. This is no April Fool joke . Confirmation can be obtained from Wagner Schlesinger, director of the Fels Planetarium of this city." This caused a panic in the city which only subsided when

13225-524: Was required for it to be used effectively. Farnsworth addressed this problem with the invention of an "electron multiplier" (not to be confused with contemporary electron multipliers ), a device that increased the number of electrons in a circuit by generating "secondary emissions" of electrons from a pair of opposed surfaces, thus amplifying the electrical signal. Farnsworth applied for a patent for his "electron multiplier" on March 3, 1930 and demonstrated its application in 1931. Farnsworth continued to improve

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