quantum mechanics · •visible light is a type of electromagnetic radiation, a form of energy that...
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Quantum Mechanics
The hidden world of the
electron
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The Wave Nature of Light
• Visible light is a type of electromagnetic radiation, a form of energy that exhibits wave-like behavior as it travels through space.
• All waves can be described by several characteristics.
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The Wave Nature of Light
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The Wave Nature of Light
• The wavelength (λ) is the shortest distance between equivalent points on a continuous wave.
• The frequency () is the number of waves that pass a given point per second.
• The amplitude is the wave’s height from the origin to a crest.
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The Wave Nature of Light
• The speed of light (3.00 108 m/s) is the product of it’s wavelength and frequency c = λ.
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The Wave Nature of Light
• Sunlight contains a continuous range of wavelengths and frequencies.
• A prism separates sunlight into a continuous spectrum of colors.
• The electromagnetic spectrum includes all forms of electromagnetic radiation.
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The Wave Nature of Light
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Shedding some light on it…
Continuous Emission Spectrum
Prism
Photographic Film
Slit
White Light
Source
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Shedding some light on it…
• Astronomical analysis of light from stars
showed dark lines in the spectra
– Absorption spectra
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The Atom and Unanswered Questions
• In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.
• Analysis of the emitted light revealed that only specific frequencies of light were emitted, not a continuous spectrum
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Shedding some light on it…
Prism
Photographic Film
Film
Slit
Low Density
Glowing
Hydrogen Gas
Discrete Emission Spectrum
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Shedding some light on it…
• Glowing gas of a single element produced
only individual lines of color
– Emission spectra
– Like a “fingerprint” for the element
• This is from hydrogen
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Shedding some light on it…
http://members.misty.com/don/spectra.html
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Energy is “quantized” in an atom
• Each line in the emission spectrum was equivalent to a specific amount of energy the atom could absorb or release
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Planck
• Planck showed that matter can only release energy as light with specific energies dependent on the temperature of the matter, not just any energy
• The minimum energy that could be released as light was called a “quantum”
• Energy could be released in whole number multiples of the “quantum” of energy – “quanta”
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Planck
• The frequency of the light that was released was proportional to the energy – Higher energy means higher frequency ()
E = h E = energy
h = Planck's constant
= frequency
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Photoelectric effect
http://www4.nau.edu/meteorite/Meteorite/Images/Photoelectric_Effect.jpg
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Einstein
• Einstein showed that light can behave as a “particle” – photoelectric effect
• A “particle” of light is called a “photon” – A mass-less particle of em energy
• The energy of the photon is proportional to its frequency
E=h
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Planck + Einstein
• The reason there was always a whole number multiple of the quantum of energy was that there was a whole number of photons released
• An atom can increase in energy when absorbing a photon of light or lower its energy when released by the atom as a photon of light