General Physics II

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General Physics II

• Applications of Quantum Mechanics

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Characteristic X-Rays

• Electrons decelerated by target - produce
  spectrum of x-rays
• Lines characteristic x-rays

Characteristic x-rays
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Characteristic X-Rays

• Inner electron of target atom knocked out of atom
• Electron from a higher level fills vacancy
• N2 fills vacancy in n1 K? line
• N3 fills vacancy in n1 K? line
• N3 fills vacancy in n2 L? line
• N4 fills vacancy in n2 L? line

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Characteristic X-Rays

• Energy of photon energy between levels as outer
  electron jumps down
• Energy calculations must take into account
  electron shielding
• Count all electrons present in lower levels

Electron in n1 shell EK -(Z-1)2(13.6eV) Electr
on in n3 shell EM -(Z-9)2(13.6eV)/n2 Ephoton
EM - EK

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Example 1

• An electron drops from the M shell (n3) to a
  vacancy in the K shell (n1) in a silver Z47
  atom. What is the change in energy Ei - Ef?

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Atomic Transitions

• Atoms can only absorb photons with energy Ehf
  matching an atomic transition (stimulated
  absorption process)
• Once electron is in an excited state, two ways of
  becoming unexcited
• Spontaneous emission (electron jumps back down on
  its own, emitting photon)
• Stimulated emission - light with energy equal to
  excitation energy incident on atom

2 photons in phase (coherent)
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LASER

• LASER - Light Amplification by Stimulated
  Emission of Radiation

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Solids

• Atoms are influenced by their neighbors
• Energy levels widen into bands interspersed by
  band gaps

Electrons have energy anywhere within the bands
gap
band
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Example 2

• When a hydrogen atom absorbs a photon that raises
  it to the n4 state, what is the greatest number
  of photons that can be emitted as it drops back
  to the ground state?