Matter and Particles of Light: Quantum Theory

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Matter and Particles of Light Quantum Theory

• Light (energy) and matter in motion behave both
  as waves and particles
• Wave-Particle Duality - Quantum Theory
• Particles of light are called photons
• Photons of a specific wavelength may be absorbed
  or emitted by atoms in matter
• Matter is made of different elements, the
  lightest one is Hydrogen
• Smallest particle of an element is atom, made up
  of a nucleus (protons and neutrons), and orbiting
  electrons

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The simplest atom Ordinary Hydrogen
p positively charged e negatively
One proton in the center (nucleus) and one
electron in orbits of definite energy Ordinary H
has no neutrons, but heavy hydrogen has one
neutron in the nucleus
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Absorption and emission of photons by H-atom
An electron may absorb or emit light photons at
specific wavelength
Wavelength (n 3 ? n 2) 6563 Angstroms (RED
Color)
Energy of the photon must be exactly equal to the
energy difference between the two orbits
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file///E/Univ7e/content/ch05/0503002.html
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Energy Level Diagram of 1H
Continuum
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Photons of all other energies (wavelengths) are
ignored and pass on by unabsorbed.
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Larger Jump More Energy Bluer Wavelength
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Energy, Frequency, Wavelength

• Light particles photons have a unique
  wavelength
• The more energetic a wave, the higher its
  frequency, or lower its wavelength
• Plancks Law Photon energy (quantum) is
• E h f h / l
• h is the Plancks constant
• This quantum of energy must be equal to the
  difference in energies between two electron
  orbits, for either absorption or emission by an
  atom

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Spectrum of a Fluorescent Light
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Characteristic spectra of elements
Each element has a unique set of spectral lines,
thus enabling its identification in the source.
Observations of spectra of different elements in
a source (planet, star, galaxy etc.) yields its
chemical composition
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Continuous, Absorption, and Emission spectra of a
source
Continuous spectrum covers wavelengths in a given
range absorption or emission spectrum consists
of dark or bright lines respectively at definite
wavelengths