quantum and nuclear physics mark lesmeister pearland isd physics

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QUANTUM AND NUCLEAR PHYSICS Mark Lesmeister Pearland ISD Physics Slide 2 Acknowledgements Selected graphics obtained from Wikipedia Commons or en.wikipedia. Their use is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license or similar license. Please see the link for each graphic for details. Slide 3 Permissions Text and original graphics Mark Lesmeister and Pearland ISD. This file and the original graphics are licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. You are free: Creative Commons Attribution-Share Alike 3.0 Unported to share to copy, distribute and transmit the work to remix to adapt the work Under the following conditions: attribution You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). share alike If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. Slide 4 PARTICLES OF LIGHT Slide 5 Infrared Videos: Bats Emerging from Caves Videos from Boston University Center for Ecology and Conservation Biology, http://www.cs.bu.edu/fac/betke/research/bats/videos.html Slide 6 Blackbody Radiation All objects emit electromagnetic radiation. The frequencies of this radiation and the amount emitted depend on the temperature of the object. Room temperature objects emit infrared frequencies. Very hot objects (like glowing coals) emit visible radiation. The universe, which has a temperature of 3 Kelvin, is awash with microwave radiation. Source: Darth Kule, Black-body.svg, http://en.wikipedia.org/wiki/File:Black_body.svg. Retrieved May 14, 2010. Graphic is public domain.http://en.wikipedia.org/wiki/File:Black_body.svg Slide 7 Quantization of Energy In the 19 th century, experiments were conducted to measure the blackbody radiation emitted at each wavelength of light. Source: Darth Kule, Black-body.svg, http://en.wikipedia.org/wiki/File:Black_body.svg. Retrieved May 14, 2010. Graphic is public domain.http://en.wikipedia.org/wiki/File:Black_body.svg Slide 8 Quantization of Energy The wave-theory of EM radiation did not agree with the experimental results for blackbody radiation. Source: Darth Kule, Black-body.svg, http://en.wikipedia.org/wiki/File:Black_body.svg. Retrieved May 14, 2010. Graphic is public domain.http://en.wikipedia.org/wiki/File:Black_body.svg Slide 9 Quantization of Energy In 1900, Max Planck developed a new theory that assumed energy isnt emitted in any amount, but only in packets, called quanta. This quantum theory agreed with the blackbody experiments. Experimental data points based on a graph from Wilson,Buffa and Lou, College Physics, Pearson Education Inc., 2010 Slide 10 Plancks Equation Plancks equation relates the energy of a quantum of light with the frequency of light. Energy = Plancks constant x frequency In atoms, energy is measured in electron volts (eV) 1 eV = 1.60 x 10 -19 J h=4.14 x 10 -15 eV-s Slide 11 Photon Practice 1 A certain radio station broadcasts a radio wave of 100 MHz and 30,000 W power. How many photons does the station emit per second? Answer: 4.5 x 10 29 photons/second Slide 12 Photon Practice 2 Two monochromatic light beams, one red and one green, have the same intensity and cover the same area. How does the energy of each photon and the number of photons in each beam compare? Photon Energy# per Second A) SameSame B) Greater for redLess for red C) Greater for redGreater for red D) Less for redLess for red E) Less for redGreater for red Slide 13 THE PHOTOELECTRIC EFFECT Slide 14 The Photoelectric Effect When light strikes a metal surface, it will give off electrons. Slide 15 The Photoelectric Effect If light is a wave, then a light beam that has greater intensity (greater energy) should cause the electrons given off to have more energy. A more intense light beam causes more electrons to be emitted, but they all have the same energy. Slide 16 The Photoelectric Effect Einstein explained the photoelectric effect by assuming that light was made of particles. A more intense light beam has more photons, but each carries the same energy. Thus, more intense light would produce more electrons, with the same energy. Slide 17 The Photoelectric Effect Slide 18 Quantum Theory of Light and the Photoelectric Effect When a photon strikes a metal plate, it transfers energy to the electrons in the plate. If an electron acquires enough energy, it can be ejected from the plate. The energy necessary to eject an electron is called the work function of the metal. The kinetic energy of the electrons will be the energy of the photon minus the work function. Slide 19 Photoelectric Effect: Practice A certain beam of light has photons with 5 eV of energy. When this light strikes a metal plate, electrons with 3 eV of kinetic energy are released. What is the work function of the metal? Answer: 2 eV Slide 20 The Cutoff Frequency Slide 21 The cut-off frequency is the frequency that produces photons of just enough energy to be emitted, i.e. equal to the work function. Photons with less energy will not be able to eject electrons. Work Function = h f Cutoff Slide 22 Wave Particle Duality In some experiments, such as blackbody radiation and the photoelectric effect, light acts like a particle (called a photon). In others, like double slit interference and thin film interference, light acts like a wave. Light never appears as both in the same experiment. Source: John- Dieselrainbow. Jpg Wikipedia Commons- Creative Commons Attribution-Share Alike 3.0 Unported license Slide 23 THE QUANTUM THEORY OF LIGHT AND THE ATOM Slide 24 Review- Electrical Potential Energy An atoms electrons are attracted to its nucleus. It requires energy to separate them. The farther away an electron is from the nucleus, the greater the energy. Slide 25 Energy Levels The electrons in an atom occupy discrete energy levels. These levels are determined by the type of atom involved. An electron gains or loses energy when transitioning between levels. Slide 26 Energy Levels We use an energy level diagram to represent the levels. Slide 27 Absorption When an atom absorbs a photon of light, an electron jumps from a lower energy level to a higher energy level. Only photons with the right amount of energy will cause an electron to jump to a higher level. Slide 28 Absorption When an atom absorbs a photon of light, an electron jumps from a lower energy level to a higher energy level. Only photons with the right amount of energy will cause an electron to jump to a higher level. Slide 29 Emission Electrons at higher levels can jump back to a lower energy level by emitting a photon. The frequency of the emitted photon is determined by the energy that the electron gave up. Slide 30 Energy Levels Electrons at higher levels can jump back to a lower energy level by emitting a photon. The frequency of the emitted photon is determined by the energy that the electron gave up. Slide 31 Emission Spectra Since the energy levels are different for each type of atom, the wavelengths of light given off by the excited electrons jumping back down are different for each type of atom. We can thus identify the atoms by the colors of light they emit. The pattern of colors is called an emission spectrum. Slide 32 Emission Spectra H Fe Source: Adrignola, Emission spectrum-H.svg Yttrium91, Emission spectrum-Fe.svg Wikipedia Commons, public domain Slide 33 Absorption Spectra When light containing all wavelengths passes through a gas, the same wavelengths of light that appear in that gas emission spectrum will be absorbed by the gas. Source: Maureen Gebruiker, Fraunhofer lines.svg Wikipedia Commons, public domain Slide 34 CONSEQUENCES OF QUANTUM MECHANICS Slide 35 Double Slit Experiment for Electrons We can carry out a double slit experiment for electrons just like Thomas Young did for light. But electrons are particles, so they wont produce an interference pattern, right? Slide 36 Double Slit Experiment for Electrons Source: Belsazar, Double-slit experiment results Tanamura 2.jpg, Wikipedia Commons, Creative Commons Attribution-Share Alike 3.0 Unported license. Slide 37 Double Slit Experiment for Electrons Electrons interfere with each other, just like waves. If we cover up one slit, the wave-like behavior goes away. Slide 38 The wave-particle duality of matter Particles of matter, such as electrons, atoms, etc., can also behave like a wave in some experiments. These matter waves are called de Broglie waves. The wavelength of these waves is given by the equation = h/p. The frequency is given by the equation f=E/h Slide 39 NUCLEAR PHYSICS Slide 40 The Nucleus An atomic nucleus consists of protons and neutron. When we want to specify a specific isotope, we write the mass number and atomic number. Slide 41 Units of Mass and Energy in Nuclear Physics In nuclear physics, mass is usually stated in terms of atomic mass units, or u. 1 u = 1.660 X 10 -27 kg Energy is usually stated in electron- volts, or eV. Particl e m (kg)m (u) Proton1.673 x 10 -27 1.007276 Neutron1.675 x 10 -27 1.008665 Electron9.109 x 10 -31.000549 1 eV= 1.602 X 10 -19 J Slide 42 Mass-Energy Equivalence Energy and mass are equivalent. Einsteins equation shows how much energy a quantity of mass corresponds to. Slide 43 Mass-Energy Equivalence Energy and mass are equivalent. Einsteins equation shows how much energy a quantity of mass corresponds to. Particlem (kg)E (MeV) Proton1.673 x 10 -27 938.3 Neutron1.675 x 10 -27 939.6 Electron9.109 x 10 -31 0.5110 1 u = 931.5 MeV Slide 44 The Strong Force The electric force would cause the protons in a nucleus to repel each other. The strong force is an attractive that overcomes the electric repulsion over small distances. Both protons and neutrons attract by the strong force. Neutrons help stabilize the nucleus. Elements with Z>83 do not have sta

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