atom and light lancelot l. kao updated: jan 24, 2010
TRANSCRIPT
Atom and Light
Lancelot L. Kao
Updated: Jan 24, 2010
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Outline
• Nature of Light• Basic Properties of Light• Three Types of Spectra• Useful Application – Doppler Effect• Atomic Structure• Periodic Table of the Elements• Interaction of Light and Matter• Blackbody Radiation• States/Phases of Matter
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Nature of Light
• What is the “Nature” of Light?
• Observed Properties of Light– reflection, refraction, diffraction, & interference
• Wave Properties– reflection, refraction, diffraction, & interference
• Particle Properties– reflection, refraction
• Particle-Wave Duality
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Wave Properties of Light
• Wave Properties– diffraction– Interference
• Young’s Double-Slit Experiment (1801)
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Wave Properties of Light
• Electromagnetic Waves– wavelength (meter)– frequency (cycles per
second = Hertz = Hz)
• Speed of Light– constant within a
medium– absolute speed– 3.0 x 108 m/s in
vacuum
Fizeau-Foucault Method (1850)
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Electromagnetic Spectrum
• Speed of Light = wavelength x frequency
• C = x
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Particle Properties of Light
• Max Planck (1900)– Blackbody Radiation– Electromagnetic energy
(radiation) is emitted in discrete, particlelike packet.
• Albert Einstein (1905)– Re-interpret Planck’s result– Photoelectric Effect– Light as particles --
photons• Energy of a Photon
– The energy of a photon is proportional to its frequency.
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Three Types of Spectra
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Interaction of Light and Matter
• Kirchoff’s 1st Law– A hot opaque body, such as a perfect blackbody, or a hot,
dense gas produces a continuous spectrum.
• Kirchoff’s 2nd Law– A hot, transparent gas produces an emission line spectrum.
• Kirchoff’s 3rd Law– A cool, transparent gas in front of a source of a continuous
spectrum produces an absorption line spectrum. The absorption lines in the absorption line spectrum of a particular gas occur at exactly the same wavelengths as the emission lines in the emission line spectrum of the same gas.
• Types of spectra of matter can produce is dictated by the physical condition/state of the matter.
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Doppler Effect
• Christian Doppler (1842)• The apparent change in wavelength or frequency of radiation due to relative
motion between the source and the observer along the line-of-sight.• If the relative motion between the source and the observer is moving away
from each other, the observed spectral line is longer than the lab wavelength, it is called a redshift. If the relative motion between the source and the observer is moving towards each other, the observed wavelength is shorter than the lab wavelength, it is called a blueshift.
c
v
o
= wavelength shift
o = lab wavelength
V = radial velocity
c = speed of light
+ = redshift
- = blueshift
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Doppler Effect
Stationary Source Moving Source
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An Example
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Relativistic Doppler Effect
cvcv
o
observed
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1
= observed wavelenght = lab wavelengthv = radial velocityc = speed of light+ = redshift- = blueshift
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Atomic Structure
• Rutherford’s Experiment (1910)
• Rutherford’s Model of the Atom
• Atomic Structure– cloud of electrons– nucleus
• protons• neutrons
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Atomic Structure
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Interaction of Light and Matter
• Bohr Model of Hydrogen Atom– energy levels or states
• Quantum Rules– Electron can only occupy at discrete energy level.– Electron can jump from one energy level to another only if it
gains or loses a specific amount of energy equal to the differences of the levels.
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Interaction of Light and Matter
Electron Transitions in Hydrogen
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Interaction of Light and Matter
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Blackbody Radiation
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Blackbody Radiation
• Wien’s Law– The wavelength of
maximum emission of a blackbody is inversely proportional to its temperature.
• Stefan-Boltzmann Law – The energy flux (power
per unit area) of a blackbody is proportional to the 4th power of its temperature.
)(
0029.0)(max KTm
42842 1067.5;)( KWmxTWmFlux
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An Example
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Interaction of Light and Matter
States of Matter