SCEN103 Class 21
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Excited States and Quantum Leaps
- State of equilibrium, state of lowest energy,
is known as the ground state
- Higher energy states are known as excited states.
- with orbitals that are larger, with different shapes.
- Electrons can be promoted to higher orbits by:
- collisions with other atoms
- bombardment with electrons or other particles
- absorption of light...
- Light is emitted when atom relaxes to ground state from excited state.
- Demonstrations of discharge lamp (with neon, hydrogen, and oxygen),
falling kg mass
- On careful examination, we find that light emitted by excited atoms
has discrete values of energy.
- Deduce that electrons in an atom have discrete values of energy.
- Energy levels of electrons in an atom are quantized.
Atomic units of energy
- In our study of electricity we measured energy in units
of kW-hr (kilowatt-hour).
- In atomic physics and semiconductor physics,
we find that the eV (electron-volt)
is a convenient unit for measuring energy of photons and electrons.
- Relationship between kW-hr and eV; eV and joule?
- A watt-second is also an acceptable unit for energy, having the same
dimensions as kilowatt-hour.
The watt-second is more commonly known as a joule (J).
- A 1 kg (kilogram) mass held overhead has about 20 J of
potential energy relative to the floor;
that is, when it hits my toe, it will be carrying
20 J of kinetic energy.
- The electron-volt is the change of energy experienced by an electron
when it is relocated from one point to another, when the two points have
a 1.0 V difference.
- The electron-volt is a small quantity compared to the joule:
1.0 eV = 1.60 x 10-19 J
The Visible Spectrum
From Marshall Space Flight Center, NASA
Additional Online References
- Visual Quantum Mechanics -- Laser Adventure
- Bohr Model of the Atom
- Energy States (Levels)
- Photons and the Energy Diagrams
- Spontaneous Emission of Electromagnetic Radiation
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Last updated April 12, 1999.
Copyright George Watson, Univ. of Delaware, 1999.