Presentation on theme: "Chapter 27 Quantum Physics. Understand the relationship between wavelength and intensity for blackbody radiation Understand how Planck’s Hypothesis."— Presentation transcript:
Understand the relationship between wavelength and intensity for blackbody radiation Understand how Planck’s Hypothesis explained the relationship between wavelength and intensity for blackbody radiation
Thermal Radiation What is it? How does it occur?
Blackbody Radiation What is it? How does it work? Graph of Intensity of BBR vs. Wavelength The Ultraviolet Catastrophe
Graph of photoelectric current vs. potential difference ( V) Current dependent on intensity Current dependent on, V
Stopping Potential KE max = e V s Independent of the radiation intensity Work Function Cutoff Wavelength c = c/ f c = hc/
Wave Theory could not explain: Cutoff Frequency KE max independent of intensity KE max increases with light frequency Electrons are emitted instantaneously Photon Theory accounts for: the work function KE max = h f – Depends only on light frequency 1 - 1interaction b/w photons and electrons Linear relationship b/w f and KE max
Photoelectric Cell Street lights Breathalyzer
Understand the nature and production of x- rays so you can: Calculate the shortest of x-rays that may be produced by electrons accelerated through a specified voltage
Wilhelm Roentgen first noticed them in 1895 while studying electrical discharges Characteristics of x-rays Traveled at or near the speed of light Were not deflected by electric or magnetic fields
In 1912 Max von Laue suggested diffracting x- rays Used atomic crystal lattice as a diffraction grating determined the wavelength of x-rays to be about 0.1 nm
The Production of x-rays Electrons are accelerated through a V of several thousand volts Electrons collide with a metal plate X-rays are the energy emitted when the electrons are decelerated, but why are they decelerated? Threshold voltage
Graph x-ray intensity vs. wavelength Continuous broad spectrum dependent on the applied voltage. Why? Characteristic spikes in the graph are dependent on the target material min = hc/(e V) Shortest wavelength radiation that can be produced
Understand the concept of Compton scattering so you can Describe Compton’s experiment, state the results, and how these results are explained Account for the increase of photon wavelength, and explain the significance of the Compton wavelength
Compton’s Experiment X-ray beam of a specified wavelength, 0, directed at a block of graphite Result was the scattered x-rays had a longer wavelength,, Amount of energy reduction depended on the angle at which the x-rays were scattered The change in wavelength, , is the Compton Shift.
Compton’s Explanation Photon particle collision similar to billiard ball collisions. Which means what? = – 0 = h/(m e c) *(1 – cos ) Compton Wavelength, h /(m e c), is very small compared to visible light.
Understand the concept of DeBroglie wavelength so they can: Calculate the wavelength of a particle as a function of its momentum Describe the Davison-Germer experiment, and explain how it provides evidence for the wave nature of electrons
Energy of a photon is converted completely into mass, pair production Electron and positron are created from a photon Energy, momentum, & charge are conserved
Minimum energy required to produce a positron h f min = 2m e c 2 ( E = mc 2 ) Pair production cannot occur in a vaccum, but can only occur in the presence of a massive particle (nucleus)
Pair Annihilation: electron-positron pair produce two photons Momentum has to be conserved
Double slit experiment shooting particles at a double slit Double slit experiment shooting particles at a double slit