PHOTOELECTRIC EFFECT - STUDENT VERSION by Lizelle Swanepoel https://padlet.com/lizellexs/f3gtc5j0ejbk GR12 en-us 2020-04-07 08:37:50 UTC 2023-02-18 18:00:03 UTC hello@padlet.com https://padlet-assets.s3.amazonaws.com/icons/Hotsun.png Einstein won the Nobel Prize - 1921 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290707 For discovering the Law of the photoelectric effect.]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290707 BACKGROUND HISTORY lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290708 Isaac Newton
“Light is a not a wave, but made of particles called a corpuscles (small discreet particles as different parts of light”. 
  • Discovered the spectrum of VIS light, as it disperses through a prism.  
]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290708 Christiaan Huygens lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290709 Dutch physicist and astronomer famous for WAVE THEORY OF LIGHT.]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290709 James Clerk Maxwell lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290710 EM Wave Theory of light. 
  • Discovered the connection between light electromagnetic waves. 
    Light consists of:
    An electric field
    A magnetic field
]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290710 Light is an EM Wave lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290711 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290711 EM Spectrum lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290713 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290713 Maxwell equations lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290714 ...and there was light]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290714 Max Planck lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290715 “The exchange of energy between light and matter only occurs in discrete amounts, called quanta.”

  • Planck constant, h = 6,62 ×10-34 J
  • h is the quantum of electromagnetic action, which relates the energy carried by a photon to its frequency. 
  • A photon's energy is equal to its frequency multiplied by the Planck constant.  E = hf
]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290715 Energy of a photon is always a “multiple” of h, depending on the frequency of light lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290716 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290716 Energy is quantized - Read this book to understand lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290717 Read to you last year in class :-)]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290717 Thomas Young lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290718 Young’s Double slit experiment
  • Light has wave-particle duality. 
  • It can act as particle or wave. 
]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290718 Double slit experiment explained lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290719 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290719 Finally Einstein lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290721 https://www.sciencelearn.org.nz/videos/51-the-photoelectric-effect]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290721 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290722 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290722 E=hf lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290725 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290725 DEMO VIDEO OF THE PHOTOELECTRIC EFFECT lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290726 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290726 Definitions lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290728
  • Frequency = The number of complete waves that pass a point per second. (measured in hertz, Hz).
  • Wavelength = The distance between two consecutive points on a wave that are in phase. (measured in metres, m)
  • Photoelectric effect = The process that occurs when electromagnetic radiation shines on a certain metal surface and it ejects electrons from the metal.
  • Photon = The quantum of energy when the energy is in the form of electromagnetic radiation. 
  • Threshold frequency (f0) = The minimum frequency of radiation at which electrons will be ejected from the surface of a certain metal.
  • Work function (W0) = The minimum energy needed to emit an electron from the surface of a certain metal.

    • ]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290728     Photoelectric Equation lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290729 Ek = hf - W0
    Ek= hf - φ

    Or:
    1/2mv2 = hf - hf0]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290729     Photoelectric effect lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290731 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290731 ANALOGY FOR WORK FUNCTION AND THRESHOLD FREQUENCY - A ROCKET LAUNCH! Escape velocity & Launch energy lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290732
    Efuel = Ek + E needed to overcome weight

    Fnet = Ffuel - Fg
    Enet = Efuel - E to overcome weight
    Ek     = Efuel - EFg

    The same happens with electrons in a metal surface when light falls onto it. 
    • If the light is of sufficient energy, then the electrons can be ejected off the particular metal surface. 
    • This is called the photoelectric effect. 
    ]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290732     Effect of wavelength of the incident photons on the kinetic energy of the ejected photoelectrons: lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290734 Recall:
    v = fλ
    So, for lightwaves:
    c = fλ
    f = c/λ

    The energy of the photons:
    E = hf
       = hc/λ

    E ∝ f
    E ∝ 1/λ

    ]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290734     Figuring out: Will electrons be ejected? lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290735 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290735 The Photocell lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290737 You must Explain its working ]]> 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290737 How can photons act as particles if they are massless? lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290738
  • Photons = packets (quanta) of light 
  • Photons are massless; m = 0

    • So how can they act as particles (as if they have mass)?
    • Photons have MOMENTUM due to Energy, and can impart their energy to electrons of any metal surface to eject them off of the surface.
    • Mass of a photon comes from its energy divided by the speed of light squared:
    • mphoton = hf/c2

    ]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290738     One electron is ejected per every one photon! lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290740 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290740 PHOTOELECTRIC GRAPHS lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290741 You need to be able to:
    • Draw a graph from relevant data.
    • Read off/determine the x-intercept. 
    • Extrapolate the graph.
    • Read off/determine the y-intercept. 
    • Calculate the gradient.
    • Interpret what gradient represents. 
    ]]>     2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290741     lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290743 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290743 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290744 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290744 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290747 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290747 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290749 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290749 TYPICAL EXAM QUESTION lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290751 2020-04-07 08:37:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496290751 Mark your work: EX 1-4 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496316396 2020-04-07 08:52:23 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496316396 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496318635 2020-04-07 08:53:36 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496318635 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496319198 2020-04-07 08:53:57 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496319198 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496319924 2020-04-07 08:54:18 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496319924 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496320862 2020-04-07 08:54:50 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496320862 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496321385 2020-04-07 08:55:10 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496321385 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496321985 2020-04-07 08:55:30 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496321985 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496322350 2020-04-07 08:55:43 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496322350 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496322720 2020-04-07 08:55:56 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496322720 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496323563 2020-04-07 08:56:23 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496323563 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496323888 2020-04-07 08:56:34 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496323888 lizellexs https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496324818 2020-04-07 08:57:06 UTC https://padlet.com/lizellexs/f3gtc5j0ejbk/wish/496324818