Presentation on theme: "QUANTUM AND NUCLEAR PHYSICS"— Presentation transcript:
1QUANTUM AND NUCLEAR PHYSICS Mark LesmeisterPearland ISD Physics
2AcknowledgementsSelected 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.
5Infrared Videos: Bats Emerging from Caves Videos from Boston University Center for Ecology and Conservation Biology,
6Blackbody 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.(1) This radiation is called “blackbody” since it does not depend on reflected light, that is, it is emitted even from perfectly absorbing objects.Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.
7Quantization of Energy In the 19th century, experiments were conducted to measure the blackbody radiation emitted at each wavelength of light.Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.
8Quantization of Energy The wave-theory of EM radiation did not agree with the experimental results for blackbody radiation.Source: Darth Kule, “Black-body.svg”, Retrieved May 14, Graphic is public domain.
9Quantization of Energy In 1900, Max Planck developed a new theory that assumed energy isn’t 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
10Planck’s EquationPlanck’s equation relates the energy of a quantum of light with the frequency of light.Energy = Planck’s constant x frequencyIn atoms, energy is measured in electron volts (eV)1 eV = 1.60 x Jh=4.14 x eV-sShow above, then do Problems 23A, p. 833.
11Photon Practice 1A 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 1029 photons/second
12Photon Practice 2Two 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 SecondA) Same SameB) Greater for red Less for redC) Greater for red Greater for redD) Less for red Less for redE) Less for red Greater for red
13The photoelectric effect Here is another example of the particle behavior of light. This photoelectric effect is behind every light sensor, digital camera, etc.The photoelectric effect
14The Photoelectric Effect When light strikes a metal surface, it will give off electrons.
15The 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.
16The 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.
18Quantum 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.
19Photoelectric Effect: Practice A certain beam of light has photons with 5 eV of energy. When this light strikes a metal plate, electrons with eV of kinetic energy are released. What is the work function of the metal?Answer: 2 eV
21The Cutoff FrequencyThe 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 fCutoff
22Wave Particle DualityIn 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“God runs electromagnetics by wave theory on Monday, Wednesday, and Friday, and the Devil runs them by quantum theory on Tuesday, Thursday, and Saturday.” - Sir William Bragg
24Review- Electrical Potential Energy An atom’s 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.
25Energy 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.
26Energy LevelsWe use an energy level diagram to represent the levels.
27AbsorptionWhen 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.
28AbsorptionWhen 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.
29EmissionElectrons 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.
30Energy LevelsElectrons 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.
31Emission SpectraSince 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.
32Emission Spectra H Fe Source: Adrignola, “Emission spectrum-H.svg” Yttrium91, “Emission spectrum-Fe.svg”Wikipedia Commons, public domain
33Absorption SpectraWhen 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
34Consequences of Quantum mechanics View video “BBT: Schrodinger’s Cat” (17:45-)Consequences of Quantum mechanics
35Double 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 won’t produce an interference pattern, right?
37Double Slit Experiment for Electrons Electrons interfere with each other, just like waves.If we cover up one slit, the wave-like behavior goes away.
38The 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 l = h/p .The frequency is given by the equation f=E/h
40The 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.
41Units of Mass and Energy in Nuclear Physics In nuclear physics, mass is usually stated in terms of atomic mass units, or u.1 u = X kgEnergy is usually stated in electron-volts, or eV.Particlem (kg)m (u)Proton1.673 x 10-27Neutron1.675 x 10-27Electron9.109 x 10-311 eV= X J
42Mass-Energy Equivalence Energy and mass are equivalent.Einstein’s equation shows how much energy a quantity of mass corresponds to.
43Mass-Energy Equivalence Particlem (kg)E (MeV)Proton1.673 x 10-27938.3Neutron1.675 x 10-27939.6Electron9.109 x 10-310.5110Energy and mass are equivalent.Einstein’s equation shows how much energy a quantity of mass corresponds to.Have the students calculate the equivalence of a kilogram of mass.1 u = MeV
44The Strong ForceThe 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 stable nuclei.
45Fundamental Forces Force Strength* Range Field Particle Strong Nuclear 1~ 1 fm = mgluonElectromagnetic10-2Infinite (1/r2)photonWeak Nuclear10-13< 10-3 fmW+,W-, and ZGravity10-38graviton* Since the forces involve different quantities and vary with distance, their strength is not a simple comparison. The answer on the homework reverses the weak nuclear and electromagnetic force relative strength.
46= + Binding Energy Binding Energy The total energy or mass of a stable nucleus is less than the mass of the individual nucleons.The difference is called the binding energy, Ebind=+ Binding Energy
47= + Binding Energy Mass Defect Since mass and energy are equivalent, the difference can also be expressed in terms of mass.The difference in mass is called the mass defect, Δm=+ Binding Energy
48Nuclear Physics Questions 1 & 2 Determine the mass defect and binding energy of deuterium.Determine the mass defect and binding energy of helium.Particlem (u)E (MeV)Proton938.3Neutron939.6DHe1 u = MeV
49Binding Energy and Nuclear Reactions Nuclear reactions involve the nuclei of atoms.If a rearrangement of protons and neutrons in a nucleus or nuclei results in a greater binding energy, the reaction will release energy.Energy
50Nuclear Physics Question 3 Determine the energy “released” when 2 deuterium combine to form a helium nucleus.Particlem (u)E (MeV)Proton938.3Neutron939.6DHe1 u = MeV
51Nuclear stabilityThe attraction of the strong force results in lower energy/nucleon for light nuclei.Because the range of the strong force is limited, beyond a certain size, binding energy/nucleon increases.Source: Fastfission, Wikipedia, public domain
52FissionIn nuclear fission, heavy nuclei split into lighter nuclei.
53Fission This may result in a chain reaction. A nuclear reactor uses a controlled chain reaction.The first “atomic” bombs were fission bombs.
54Fusion Light nuclei can undergo fusion. Fusion is the nuclear reaction that powers the sun.Researchers are trying to develop a fusion reactor that releases more energy than it uses.Source: Wykis, “Deuterium-tritium fusion.svg” Wikipedia Commons, public domain
55Nuclear Physics Question 3 Correct statements about the binding energy of a nucleus include which of the following:I) It is the energy needed to separate the nucleus into its individual nucleons.II) It is the energy liberated when the nucleus is formed from the original nucleons.III) It is the energy equivalent of the apparent loss of mass of its nucleon constituents.A) I only. B) III only.C) I and II only. D ) II and III only.E) I, II, and III
57What is your radiation dose? Calculate Your Radiation Dose | Radiation Protection | US EPA
58Nuclear DecayAn unstable nucleus can break apart into other particles, releasing energy.This process occurs naturally in hundreds of types of nuclei.++ Energy
59Nuclear RadiationThree types of radiation are emitted in radioactive decay.ParticleSymbolCompositionChargeEffect on ParentAlpha2 protons,2 neutrons(He nucleus)+2Less mass, new elementBetaelectronpositron-1+1~same mass, new elementGammaphotonEnergy lossBased on “Holt Physics, Table 25-3, p. 903
60Uses of nuclear radiation Carbon datingChemical tracingRadiation therapyFood irradiationSterilization of medical equipmentNon-destructive testingSmoke detectorsSecurity scanningNuclear power
61Carbon DatingSome atmospheric carbon is C-14, produced by cosmic rays.
62Carbon DatingThis carbon-14 naturally decays to nitrogen with beta decay.-