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Unformatted text preview: Lecture 5 -- Light and Matter
Outline: Experiencing light Interaction of light and matter EM spectrum Properties of matter Read sections 5.1 - 5.4 in textbook. Last time The standard model; particle zoo, Fermions and bosons, Exchange particles, Uncertainty principle, Exclusion principle, Virtual particles Fundamental Particles Electron Waves How do light and matter interact? Emission Absorption Transmission Transparent objects transmit light Opaque objects block (absorb) light On atomic scales, an electron often behaves more like a wave with a well-defined momentum but a poorly defined position. Reflection or Scattering Reflection and Scattering Interactions of Light with Matter A mirror reflects light in a particular direction. A movie screen scatters light in all directions. Interactions between light and matter determine the appearance of everything around us Thought Question Why is a rose red?
a) b) c) d) The The The The rose rose rose rose absorbs red light. transmits red light. emits red light. reflects red light. a) b) c) d) Thought Question Why is a rose red?
The rose absorbs red light. The rose transmits red light. The rose emits red light. The rose reflects red light. Waves A wave is a pattern of motion that can carry energy without carrying matter along with it. Properties of Waves Wavelength and Frequency Wavelength is the distance between two wave peaks Frequency is the number of times per second that a wave vibrates up and down. wave speed = wavelength x frequency wavelength x frequency = speed of light = constant Particles of Light Particles of light are called photons Each photon has a wavelength and a frequency The energy of a photon depends on its frequency. Wavelength, Frequency, and Energy
!x f = c ! = wavelength , f = frequency c = 3.00 x 108 m/s = speed of light E = h x f = photon energy h = 6.626 x 10-34 joule x s = photon energy Light: Electromagnetic Waves Colors of Light A light wave is a vibration of electric and magnetic fields, Light interacts with charged particles through these electric and magnetic fields. White light is made up of many different colors. What is the electromagnetic spectrum? What is the structure of matter?
Electron Cloud Atom Nucleus Atomic Terminology Atomic Number = # of protons in nucleus Atomic Mass Number = # of protons + neutrons Atomic Terminology Isotope: same # of protons but different # of neutrons. (4He, 3He) Molecules: consist of two or more atoms (H2O, CO2) What are the phases of matter? Familiar phases: Solid (ice) Liquid (water) Gas (water vapor) Phases of Matter Phases of same material behave differently because of differences in chemical bonds. Phase Changes Ionization: Stripping of electrons, changing atoms into plasma Dissociation: Breaking of molecules into atoms Evaporation: Breaking of flexible chemical bonds, changing liquid into solid Melting: Breaking of rigid chemical bonds, changing solid into liquid. Phases and Pressure Phase of a substance depends on both temperature and pressure Often more than one phase is present. How is energy stored in atoms? Energy Level Transitions The only allowed changes in energy are those corresponding to a transition between energy levels. Excited States Ground State Electrons in atoms are restricted to particular energy levels. Not Allowed Allowed ...
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- Fall '07