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UH PHYS 1302 - Exam3Review_2015

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Exam 3 ReviewDr. Anthony Timmins30-1 Blackbody Radiation and Planck’s Hypothesis of Quantized Energy• Blackbody: perfect absorber and emitter of radiation… • Peak emission frequency given by: • Inconsistent with classical physics theory… • Radiation energy needed to be quantized to describe data…30-2 Photons and the Photoelectric EffectEinstein suggested quantization was needed because radiation consists of many small particles… -Photons…Study of the photoelectric effect supported this… -Minimum frequency (f0) needed to liberate electrons… -Light with f < f0 no matter how intense won’t liberate electrons…30-3 The Mass and Momentum of a Photon•…Even though photon has zero mass, it has finite momentum…30-4 Photon Scattering and the Compton Effectλλ’Demonstrates particle like behavior of waves…mass of electron30-5 The de Broglie Hypothesis and Wave-Particle DualityWave like properties of particles have been confirmed many times over e.g. diffraction pattern of electrons…Since waves (photons) can act like particles… ….Particles should be able to act like waves…30-6 The Heisenberg Uncertainty PrincipleIf one tries to know position of electron by making it pass through narrow slit… Diffractive properties of particle means there’s an uncertainty in the momentum… Applies to energy/time too…30-7 Quantum TunnelingWaves can tunnel through gaps… Since particle can act as waves,they can tunnel as well… Application is the scanning tunneling microscope, which can image single atoms using the tunneling of electrons…31-1 Early Models of the Atom• First modern model of the atom was therefore the “plum pudding” model • Looked alpha particles scattering from gold foil: - Found many more large-angle scatters than expected… - Only happen if the positive charge were concentrated in a tiny volume…31-2 The Spectrum of Atomic Hydrogen• Each atom has particular pattern of emission / absorption lines… •Hydrogen atom shown left -Described by Balmer series:31-3 Bohr’s Model of the Hydrogen AtomElectron in a hydrogen atom moves in a quantized circular orbits Angular momentum in the nth allowed orbit is Photon emitted when an electron changes from one orbit to another:Radius of nth orbitTotal energy of nth orbit31-4 de Broglie Waves and the Bohr ModelDe Broglie proposed allowed orbits were those which of the electron had integer wavelengths of:31-5 The Quantum Mechanical Hydrogen AtomMore advanced description: requires 4 quantum numbers: 1. The principal quantum number gives the energy of the electron, n 2. The orbital angular momentum quantum number l 3. The magnetic quantum number ml 4. The electron spin quantum number ms31-6 Multi-electron Atoms and Periodic Table Two electrons can never have the same set of quantum numbers Adding more electrons means they generally have higher energy:31-7 Atomic RadiationFluorescence occurs when electrons emit photons of various frequencies when returning to the ground state.32-1 The Constituents and Structure of NucleiNucleus has: A number of nucleons, Z number of protons, N number of neutrons. Radius of nucleus:E.g…Mass units…32-1 The Constituents and Structure of NucleiNucleus contains positive charges, why doesn’t it fly apart due to mutual repulsion? • Another force acting, called the strong nuclear force • Keeps nucleus together... • Short range, acting only to distances of a couple fm. • Always attractive… • Acts with nearly equal strength between proton-proton, proton-neutron, and neutron-neutron…32-2 RadioactivityUnstable nuclei can either decay in 3 ways via emission of: 1.Alpha particles, two neutrons and two protons 2.Electrons and positrons (beta rays) 3.Gamma rays, which are high-energy photons.32-2 RadioactivitySome nuclei decay more rapidly than others. The rate of decay – the number of decays per second – is called the activity. Two units of activity:The curie (and the millicurie and microcurie) are most commonly used.32-3 Half-Life and Radioactive DatingNumber of nuclei that haven’t decayed (I.e. remain radioactive) after time t is: N0 is initial number of radioactive particles… Half life: time it takes for half a sample to decay away. Decay rate, or activity, is also related to the decay constant:32-4 Nuclear Binding EnergyMass of any stable nucleus is less than the sum of the masses of the protons and neutrons it contains: •Difference, multiplied by c2, called binding energy • Can be expressed as the binding energy per nucleon32-5,6 Nuclear Fission and FusionNuclear fission: - Occurs when a heavy nucleus splits into two lighter ones.Nuclear fusion: very light nuclei combine to form a heavier nucleus - Smaller mass per nucleon, energy released. - Can only occur at extremely high temperatures I.e. stars.32-7 Practical Applications of Nuclear PhysicsCharged released via radiationEnergy released via radiation32-8 Elementary ParticlesLeptonsHadronsQuarksBaryon = 3 quarks Meson = quark and anti-quark16-1,2 TemperatureThe zeroth law of thermodynamics: If object A is in thermal equilibrium with object B… Object C is also in thermal equilibrium with object B Objects A and C will be in thermal equilibrium if brought into thermal contact.All objects have the same Temperature and heat cannot be transferred between themConverting between Fahrenheit and Celsius :16-3,4 Thermal Expansion and Mechanical workMost substances expand when heated; the change in length or volume is typically proportional to the change in temperature.One kilocalorie (kcal) is defined as the amount of heat needed to raise the temperature of 1 kg of water from 14.5° C to 15.5° C.16-5 Specific HeatsHeat capacity of an object is the amount of heat added to it divided by its rise in temperature:Q is positive if ΔT is positive Heat is added to a system. Q is negative if ΔT is negative Heat is removed from a system.16-6 Conduction, Convection, and RadiationConduction, convection, and radiation are three ways that heat can be exchanged. Conduction is the flow of heat via a material… Convection is the flow of fluid Radiation is the transfer via photons17-1 Ideal GasesDescribes gases with no inter-molecule interactions:Another version:n = number of moles, R = 8.31 J/(K•mol)17-2 Kinetic TheoryKinetic theory relates microscopic quantities (position, velocity) to macroscopic ones (pressure, temperature). Add up all energies to get:17-5 Latent HeatsWhen two phases coexist,


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