Physics 19 – Photoelectric Effect. Overview: In , Heinrich Hertz discovered that when electromagnetic radiation shines on a clean, metal surface, electrons. PDF | The photoelectric effect is commonly used as the introductory topic for the study of quantum physics. However, a literature review reveals. Photoelectric effect: experiment showing light is also a particle. Energy comes in particle-like chunks- basics of quantum physics. (energy of one chunk depends.
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Photoelectric effect. 1 Background. A photon of frequency ν carries energy hν, where h is Planck's constant. If such a photon strikes an electron inside a metallic . Experimental Set-up to study Photoelectric Effect. 4. Effect of Intensity, Frequency, Potential on P.E. Current. 5. Graphical representation of variation of P.E. Albert Einstein ( - ) published his theory of the photoelectric effect in , the same year in which he published the Special Theory of.
Sunlight is not rich in ultra-violet rays, as these have been absorbed by the atmosphere, and it does not produce nearly so large an effect as the arc-light. Many substances besides metals discharge negative electricity under the action of ultraviolet light: lists of these substances will be found in papers by G. Schmidt  and O.
In , Willoughby Smith discovered photoconductivity in selenium while testing the metal for its high resistance properties in conjunction with his work involving submarine telegraph cables.
His receiver consisted of a coil with a spark gap , where a spark would be seen upon detection of electromagnetic waves. He placed 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 the glass with quartz, as quartz does not absorb UV radiation. Hertz concluded his months of investigation and reported the results obtained.
He did not further pursue the investigation of this effect. The discovery by Hertz  in that the incidence of ultra-violet light on a spark gap facilitated the passage of the spark, led immediately to a series of investigations by Hallwachs ,  Hoor,  Righi  and Stoletow        on the effect of light, and especially of ultra-violet light, on charged bodies. It was proved by these investigations that a newly cleaned surface of zinc, if charged with negative electricity, rapidly loses this charge however small it may be when ultra-violet light falls upon the surface; while if the surface is uncharged to begin with, it acquires a positive charge when exposed to the light, the negative electrification going out into the gas by which the metal is surrounded; this positive electrification can be much increased by directing a strong airblast against the surface.
If however the zinc surface is positively electrified it suffers no loss of charge when exposed to the light: this result has been questioned, but a very careful examination of the phenomenon by Elster and Geitel  has shown that the loss observed under certain circumstances is due to the discharge by the light reflected from the zinc surface of negative electrification on neighbouring conductors induced by the positive charge, the negative electricity under the influence of the electric field moving up to the positively electrified surface.
According to an important research by Wilhelm Hallwachs , ozone played an important part in the phenomenon. It was at the time not even sure that the fatigue is absent in a vacuum. In the period from February and until , a detailed analysis of photo effect was performed by Aleksandr Stoletov with results published in 6 works;       four of them in Comptes Rendus , one review in Physikalische Revue translated from Russian , and the last work in Journal de Physique.
First, in these works Stoletov invented a new experimental setup which was more suitable for a quantitative analysis of photo effect. Using this setup, he discovered the direct proportionality between the intensity of light and the induced photo electric current the first law of photo effect or Stoletov's law.
One of his other findings resulted from measurements of the dependence of the intensity of the electric photo current on the gas pressure, where he found the existence of an optimal gas pressure Pm corresponding to a maximum photocurrent ; this property was used for a creation of solar cells. Thomson investigated ultraviolet light in Crookes tubes.
In the research, Thomson enclosed a metal plate a cathode in a vacuum tube, and exposed it to high-frequency radiation. The amount of this current varied with the intensity and color of the radiation.
Larger radiation intensity or frequency would produce more current. 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 did J.
Thomson, as a Hertz effect upon the solid or liquid particles present in the gas.
Experimental study of photoelectric effect
Lenard observed the variation in electron energy with light frequency using a powerful electric arc lamp which enabled him to investigate large changes in intensity, and that had sufficient power to enable him to investigate the variation of potential with light frequency.
His experiment directly measured potentials, not electron kinetic energy: he found the electron energy by relating it to the maximum stopping potential voltage in a phototube. He found that the calculated maximum electron kinetic energy is determined by the frequency of the light. For example, an increase in frequency results in an increase in the maximum kinetic energy calculated for an electron upon liberation — ultraviolet radiation would require a higher applied stopping potential to stop current in a phototube than blue light.
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 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.
The researches of Langevin and those of Eugene Bloch  have shown that the greater part of the Lenard effect is certainly due to this 'Hertz effect'.
The Lenard effect upon the gas[ clarification needed ] itself nevertheless does exist. Refound by J. Thomson  and then more decisively by Frederic Palmer, Jr. Based upon Max Planck 's theory of black-body radiation , Einstein theorized that the energy in each quantum of light was equal to the frequency multiplied by a constant, later called Planck's constant. A photon above a threshold frequency has the required energy to eject a single electron, creating the observed effect.
This discovery led to the quantum revolution in physics and earned Einstein the Nobel Prize in Physics in This paper proposed the simple description of "light quanta", or photons, and showed how they explained such phenomena as the photoelectric effect.
His simple explanation in terms of absorption of discrete quanta of light explained the features of the phenomenon and the characteristic frequency. By assuming that light actually consisted of discrete energy packets, Einstein wrote an equation for the photoelectric effect that agreed with experimental results.
It explained why the energy of photoelectrons was dependent only on the frequency of the incident light and not on its intensity: at low-intensity, the high-frequency source could supply a few high energy photons, whereas a high-intensity, the low-frequency source would supply no photons of sufficient individual energy to dislodge any electrons. This was an enormous 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 for electromagnetic behavior, and more generally, the assumption of infinite divisibility of energy in physical systems.
Even after experiments showed that Einstein's equations for the photoelectric effect were accurate, resistance to the idea of photons continued since it appeared to contradict Maxwell's equations, which were well understood and verified.
Einstein's work predicted that the energy of individual ejected electrons increases linearly with the frequency of the light.
Perhaps surprisingly, the precise relationship had not at that time been tested. By 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 when Robert Andrews Millikan showed that Einstein's prediction was correct.
Light simultaneously possesses the characteristics of both waves and particles, each being manifested according to the circumstances. Thus photoelectric effect is instantaneous. Therefore no emission is possible if v v. Thus photoelectric current increases with intensity. But vmax remains constant. Photoelectric cells A photoelectric cell is a device which converts light energy into electrical energy.
There are three types of photoelectric cells. This layer is light sensitive and acts as the cathode c of the cell.
A small portion of the tube is transparent to allow the light to enter the tube. The anode in the form of thin wire A of platinum or nickel is mounted inside the tube. C is connected to the negative terminal and A to the positive terminal of a variable DC voltage source of 80 to V through a resistance R. When light of frequency higher than the threshold frequency falls on the cathode C, photelectrons are emitted.
These electrons are attracted by the anode A and so a current flows in the external circuit. Photoemissive cells are used in exposure meters, cinematography, etc. This layer is covered with a thin film of silver or gold which is practically transparent.
When light falls on the oxide layer move towards the silver film.For a given metal, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This work will tray about this.
Time-delayed photoelectric effect
The charged dust then repels itself and lifts off the surface of the Moon by electrostatic levitation. Thomson, as a Hertz effect upon the solid or liquid particles present in the gas.
But if we suppose that I could find one light frequency to the anode and I could generate electric current?
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