What is Photoelectric effect: Definition and 393 Discussions

The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid state and quantum chemistry to draw inferences about 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 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 could not build up the energy required to produce photoelectrons like it would have if light's energy was coming 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.
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 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, the photovoltaic effect, and the photoelectrochemical effect.

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  1. F

    I Photoelectric effect and Saturation Current

    Hello, I understand the photoelectric effect, its importance, and the basic theory. But I have a few questions: 1) One photon "can" free only a single electron, correct? However, it is not certain that if we shine exactly 10 photons (frequency? ##f_0##), that 10 photoelectrons will be free...
  2. P

    I Question about the Photoelectric Effect and the Work Function of a Metal

    By the results of the photoelectric effect experiment, the photoelectric effect does not occur at all if the frequency of the light source is below a certain value. We have the Work Function for a metal. Why when the energy of the photons of the light source is W/2, we don't have the...
  3. cemtu

    I K-Shell, Low-Energetic Photons & Photoelectric effect

    At low photon energies, the probability of the photoelectric effect to occur increases, but the probability of the photoelectric effect to happen also increases when going towards most inner shells like K shell but inner shells require much more photon energies to be broken, so isn't there a...
  4. S

    Photoelectric effect confusion

    We know that electrons bound to an atom can only absorb light with certain energies that match the energy difference between two energy levels or otherwise this implies electrons can exist in between energy levels. Then electrons will spiral into the nucleus due to the attractive forces between...
  5. J

    I Is there a Crookes radiometer device with photoelectric effect?

    https://en.wikipedia.org/wiki/Crookes_radiometer WOuld it rotate faster if I use plaques with different materials where we get the photoelectric effect in one of them?
  6. mgcgian

    I Photoelectric effect: Saturation voltage

    Hi, I just got two inquiries: My understanding is that the saturation current is reached when the intensity of light is fixed, when the potential difference is at its positive maximum magnitude. Subsequently, whatever kinetic energy store of any photoelectrons, however deep within the metal's...
  7. in2infinity

    B The wave solution to the Photoelectric effect

    I was recently examining the relationship between the work function of a material and its threshold wavelength. It was clear to me that the relationship is expressed as: (λW)² = c/2 Where λ is the threshold wavelength, W is the work function, and c is the speed of light. However, I am unable...
  8. R

    B Is it possible to get the photoelectric effect in red color frequency?

    Is it possible to get the photoelectric effect in red color frequency?
  9. P

    I What were the real results of the photoelectric effect experiment?

    Pearson Physics 12 states: "When the light sources have the same intensity but different frequencies, they produce the same maximum current" However, Phet Simulation Photoelectric Effect seems to show that photocurrent changes with light frequency (eg see below for different photocurrents at...
  10. Aurora_b

    What is the common error when discussing the photoelectric effect?

    I would believe the last statement if Intensity only depended on N but it also depends on the frequency f. Now if Intensity depends on f we can also find a relationship between KE_max and Intensity by substituting from eqn 2) in eqn 1) KE_max = IA/N - W So if KE_max depends on f and I depends...
  11. qnt200

    B Why is there now evidence of a lag time in the photoelectric effect?

    From: https://opentextbc.ca/universityphysicsv3openstax/chapter/photoelectric-effect/ "The photoelectric effect has three important characteristics that cannot be explained by classical physics: (1) the absence of a lag time, (2) the independence of the kinetic energy of photoelectrons on the...
  12. B

    Photoelectric Effect Classical Breakdown

    So I'm kind of confused about how to interpret the question and the idea of there being a small enough ##\tau## for the classical picture to break down. I started with the max KE eqn: ##KE_{max} = E_{incoming} - \phi## I suppose ##E_{incoming}## is the power (W) times time and that is also...
  13. docnet

    A basic question about Photoelectric effect

    The energy of a photon with wavelength ##\lambda=500nm## is given by the equation ##E_{photon}=h\nu=\frac{hc}{\lambda}##. ##E_{photon}=3.614\times10^-19 J=2.256eV## The kinetic energy of an ejected photo-electron is given by ##KE_{electron}=E_{photon}-Work## Using the given ##\lambda## and...
  14. R

    I Some questions about the photoelectric experiment

    Background: self-studying. Very confused. Here are some initial questions I have about the photoelectric experiment. Some more may pop up later. 1. The book says we know photons exist due to energy considerations (such as emission or absorption). They also say that this photon energy is...
  15. R

    Can infrared photons also eject electrons in 'photoelectric effect'?

    Hello, I have this question whether it will be possible to generate electricity by heating up a suitable metal (conductor). We know from the photoelectric effect that high energy photons (of visible light; probably with frequency closer to that of violet) can knock off the outer electrons from...
  16. K

    Photoelectric effect and continuous energy function

    E=hf-W where W is a work function. However we know that electrons in an atom will be excited only when radiated with photons of n*f0 discrete number of frequencies. where E=hf-W is a continuous function. Is this because energy level is continuous within a conductor? If we think of only...
  17. AN630078

    Photoelectric Effect Graph and Work Function Questions

    1. a)I have plotted the graph on desmos and attached an image here. b i. The threshold frequency is equal to the x-intercept ~ 5.6*10^14 Hz ii. The work function is equal to the y-intercept ~ -3.75*10^19 J (would it be correct to state that this value is negative?) c. Convert to eV; 3.75*10^19...
  18. thaiqi

    Are there articles on Classical computation of the Photoelectric Effect?

    photoelectric effect is now explained in quantum idea. Why the classical model fails? Are there articles computing it in detail using classical model?
  19. Rongeet Banerjee

    What is the definition of cathode in the photoelectric effect?

    We know anode=oxidation=loss of electrons and cathode=reduction=gain of electrons but in the photoelectric effect the electrons are gained at the anode and lost at the cathode of the discharge tube? References: Anode, Cathode, Oxidation, Reduction
  20. J

    Photoelectric Effect questions to help my understanding

    Homework Statement:: This isn't homework, I didn't know exactly where to post my question so I thought it would be safest to post here. Relevant Equations:: N/a My questions are as follows: 1. When the voltage is increased to a certain value the current between the two plates(emitter plate)...
  21. T

    A Photoelectric effect at metal junctions

    Any idea about difference in photoelectric effect between a piece of pure metal and that metal connected at one end with another metal. Would the work function of the metal with photoelectric effect differ in the latter case?
  22. Manasan3010

    I Exploring the Physics of Photoelectric Cells: Electrons, Energy & Color

    In this article, writer says that when atom is hit by photon it gets excited and expelled out of atom and this can be used to form images. My questions are: Why didn't the electrons get to a higher energy level, instead of getting knocked out? How do we find the color(frequency of wave) using...
  23. B

    Increase Photocell Illumination: Effect on Current

    as intensity is power per unit area and as power is proportional to energy, then increasing intensity increases energy of the photons?no? So if energy increases so will the speed of the electrons more energy to the kinetic energy after work function? the answer is current
  24. Zeynaz

    Calculating Electron Emission and Reflection in the Photoelectric Effect

    The full questions is in the picture. I already solved a) and found 5.6E14 electrons per second For b) i first found the power of the light but just multiplying the intensity with the area: (6.0 W/m2)(3.5E-4 m^2) = 0.0021 W Then I tried to use the voltage from the graph but i am not sure which...
  25. G

    A Frequency threshold in the photoelectric effect

    The existence of a frequency threshold in the photoelectric effect is often regarded as the strongest objection to the wave theory. Because?
  26. B

    Photoelectric Effect versus Laser Stimulated Emission [Confused]

    Our teacher taught us "Laser" today and it made me confused. So Electron s energy in n=1 is around 13 eV (-13eV) and in n=2 is around -3.4 eV. Our teacher told us if we radiate a photon which has 9.6 eV energy (the difference energy of the first and second layer, n1 and n2, which is 13-3.4=9.6...
  27. Boltzman Oscillation

    Classical Book for research of the photoelectric effect?

    Hi, I am not sure if this is the right place to post this but i need help finding resources for the photoelectric effect? I need to write a research paper but I do not know what I could read. The paper is for an undergrad physics course so I don't need much detail, I just need to explain the...
  28. Sandeep T S

    I Energy of a Wave & the Photoelectric Effect: Is My Statement Correct?

    In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.
  29. J

    B Ultraviolet Catastrophe & the Photoelectric Effect

    Hi, Please could somebody verify if what I have understood about the UV catastrophe is along the correct lines. I used this hyperphysics link: (http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html) Is it saying that using classical physics an object like a pen should be emitting just as much...
  30. volnei_cipriano

    Photoelectric effect in the study of a luminous diode (LED)

    I have studied the operation of light Diodes in the basic electronics course in my graduation and I had a question! Light Diodes (LEDs) are semiconductor materials with P-N junctions and that when energized emit visible light. I understand that the process of light emission when applying a...
  31. Sandeep T S

    I Photoelectric effect questions: photon absorption and electron ejection....

    Is a photon fully absorbed by a electron in metal? Ejected electron is a free electron or bonded one? Is it possible to have a zero work function? If not why? I want to study about this detaily ,can you prefer some reference papers?
  32. Zahid Iftikhar

    I Ejection of Only one electron by a Photon in the Photoelectric effect

    Hi I am surprised to know why only one photon in photoelectric effect ejects one electron only. What if a high energy photon (not necessarily x-ray or gamma ray, which may cause Compton effect or pair production)hits the metal, say it has energy double or triple of that of the work function? Why...
  33. T

    I Photoelectric absorption and low energy electron absorption

    I have am currently reading Radiation Detection and Measurement, by Gleen F.Knoll, and in chapter 10 page 309. And have come across something that is causing a bit of confusion, for context the chapter is on gamma ray spectroscopy. So in the text it say's 'Thus the effect of photoelectric...
  34. MeAndMyLucidLife

    Photo-current and Intensity of light

    Homework Statement If the frequency and intensity of a light source are both doubled, show that the saturation photo-current remains almost the same. 2. Relevant Graph https://cnx.org/resources/e73bf218926bd39de4a52bafe3a82d04bbf73542/CNX_UPhysics_39_02_photoexp1.jpg The Attempt at a Solution...
  35. Shivam

    Does the Photoelectric Effect Prove the Particle Nature of Light?

    It is said that photoelectric effect of light proves that light has particle nature, but which property is shown by light in the photoelectric effect which is also the property show by things having particle nature? Even in the photoelectric effect the energy is transferred in the form of wave...
  36. P

    Photoelectric effect, calculating work function

    Homework Statement (Given a voltage against frequency graph) Calculate the work function of Sodium and state any assumptions you have made. My question is, what assumptions have I made? Homework Equations hf = work function V = IR The Attempt at a Solution I know on a Voltage against...
  37. B

    A Photoelectric Effect via QED?

    Chapter 5 of this book: https://www.amazon.com/dp/0750633719/?tag=pfamazon01-20 as one can see in the table of contents preview, discusses the photoelectric effect starting from the first principles of quantum field theory developed in the earlier chapters. I can't find another qft book which...
  38. Safder Aree

    How to approach this photoelectric effect question

    I am currently taking my first Quantum Mechanics course and was given this problem in a practice set(we are supposed to refer to old intro textbooks). We haven't covered the photoelectric effect (just theory) much in class and reading through other textbooks, I wasn't able to find any similar...
  39. F

    Saturation voltage for photoelectric current

    Hi, I was wondering about saturation current in the photoelectric effect. It is clear to me that for a sufficiently large accelerating potential all of the electrons are gathered by the collecting electrode. Since it is all of them, there cannot be more, and the current won't change if the...
  40. D

    Question about the photoelectric effect

    1. The question asks why the photodiode is less than 100% efficient.2. hf=work function+KEmax 3.- I reckon this is as some light will not cause e to be emitted if the wavelength of the light is less the needed. -Or some photons will not hit any electron. Is this correct? Thinking about this...
  41. T

    Photoelectric effect , Superposition of sine waves

    Homework Statement In a photoelectric effect experiment, a monochromatic plane wave of light falls on a metal plate. The electric field in the light wave at a point near the plate varies according to E=E_0 \cos (\omega t). This results in a saturation current of 6 μA. If instead, the light wave...
  42. spareine

    Is the photoelectric effect in a photocell reversible?

    Is the photoelectric effect in a photocell reversible? Suppose both the cathode and the anode of a photocell are from cesium. The anode and the cathode are externally (outside the photocell) connected by a copper wire. Cesium has a threshold frequency of 470 THz. The cathode is illuminated with...
  43. G Cooke

    Conservation of electrical energy on a conductor

    I'm having trouble seeing how electric potential energy production on a conductor follows conservation of energy. Let's use the photoelectric effect as an example. A photon with energy E = hν strikes a conductor, ejecting a photoelectron with a maximum kinetic energy of hν - φ. Assuming the...
  44. E

    Photoelectric Effect: Find K.E. of Photoelectron in Air, Cs-137

    Homework Statement The gamma photon emitted by the nucleus of the cesium isotope with 137 mass number is absorbed with photoeffect. The absorbing medium is air, assume the work function to be 34 ev. What will be the kinetic energy of the photoelectron in eV? Homework Equations hf=K+Φ The...
  45. F

    Does this formula exist? (ν' = En/hc)

    ν' = En/hc ? ν' is the wavelenght's number (in electromagnatique radiation) where ν' = 1/λ if so, how do we get it ?
  46. C

    Does charging metal negatively decrease the work function?

    Since positive charge on the photocatode increases work function of electrons, does charging metal photocatode negatively decrease work function? If not, why?
  47. A

    B Planck-Einstein relation and the Photoelectric Effect

    Hi everyone, I just have some confusion regarding Planck's and Einstein's equation. The following is an explanation of the photoelectric effect using Einsteins theory: Light is composed of photons. Each photon has energy hf and mass hf/c^2. When ultraviolet photons are brought to rest by zinc...
  48. Pushoam

    The effect on a photocurrent of reducing the frequency of photons

    Homework Statement Homework EquationsThe Attempt at a Solution As frequency is decreased to threshold, no. of emitted electrons will remain same, but their maximum kinetic energy will decrease. So, the current should decrease slowly. For frequency less than the threshold frequency, no...
  49. T

    Kinetic energy of recoil atom in the photoelectric effect

    Homework Statement In the photoelectric effect it is generalley assumed that all the energy is given as kinetic energy to the electron while the atom is neglected. Do not neglect the recoil kinetic energy of the atom and calculate the kinetic energy of the photoelectron and the ionized atom and...
  50. S

    How can I find the maximum KE of the photoelectrons?

    Homework Statement I don't know how to do Question 2 part C. Homework Equations I know that E=hf and I know the photoelectric equation: hf = work function + 1/2mv^2The Attempt at a Solution I honestly don't have a clue how to do part c of question 2. I think it involves one of the two...