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Dual Nature of Light

  • Photoelectric effect: when light falls on a metal surface, electrons are emitted with kinetic energy K.
  • Some experimental facts:
    • The maximum value of K is independent of the light intensity.
    • No electrons are emitted if the incident photon frequency is below a threshold value.
    • K increases with increasing photon frequency.
  • Einstein’s explanation:
    • Light is a stream of quanta (photons). Each photon has energy E = hf, where h is Planck’s constant and f is the frequency.
    • A photon gives all its energy to a single electron.
    • K_max = hf – W, where W is the work function.
  • Compton scattering: when a photon is scattered from an electron, a change in wavelength of the photon takes place.

Dual Nature of Light

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Photoelectric Effect 0:13
    • Shine Light on Metal Surface
    • Another Metal Surface Both Enclosed and Connected to Battery
    • Connecting Ammeter to Read Current
    • Connecting a Variable Voltage
    • Negative Voltage Has Stopping Potential
  • Features of Photoelectric Effect 20:44
    • Dependence on Intensity
    • Energy Carried By Wave Proportional to Intensity
    • Kinetic Energy
    • Dependence of Photoemission on Time
    • Dependence on Frequency
    • Measuring Maximum Kinetic Energy
  • Einstein and the Photoelectric Effect 31:21
    • Stream of Quantum Particles
    • Dim Blue Light, Few Photons
    • Bright Red Light, Many Photons
    • Electron is Bound to Surface of Metal
  • Example 44:20
    • Incident Light 200 nm
  • Compton Scattering 50:22
    • Shooting X-Rays at Targets
    • Photons Colliding with Electrons
    • Compton Wavelength of Electron
  • Example 57:25
    • Lambda=0.1nm
  • Extra Example 1: Photoelectric Effect
  • Extra Example 2: Different Frequency Radiation