PHY122_L23 - PHY122 Physics for the Life Sciences II...

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PHY122 – Physics for the Life Sciences II Lecture 23 Atomic and Molecular Physics Note: Clicker Channel 21 11/29/2011 Lecture 23 1
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Summary Quantum Physics Photons: – light QUANTA with energy E=hf=hc / λ , with hc= 1240 eV·nm – proof: from the Photoelectric Effect (sub)Atomic particles exhibit wave character : –momen tum wavelength: p=h / λ – the particle system has an associated wave function ψ (r) – wave function squared | ψ (r)| 2 describes the probability for finding a particle at position r . consequences: – mono-energetic light ánd particle beams both exhibit INTERFERENCE and diffraction … –Thus : when CONFINED (e.g. in box of length L ), the system shows DISCRETE energy/momentum levels • e.g. for particle in a box: E n =n 2 h 2 /(8 mL 2 ) transitions between energy states via emission and absorption of photons of energy equal to the energy level difference • going from the quantum to the classical regime: n large 11/29/2011 Lecture 23 2
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The de Broglie Relationship states that … 11/29/2011 Lecture 23 3 1234 27% 10% 55% 8% 1. the product of uncertainties in momentum and position in a given direction must be larger or equal to h /4 π 2. stable atomic orbits are determined by the relation 2 π r=n λ , n= 1,2,3, 3. a particle’s momentum and wavelength are inversely related 4. a photon’s energy and frequency are proportional to one another …
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BoundParticles and Energy Quantization When a particle is “ confined ” … – e.g. an electron attached to an atom – or a particle in a “box” of length L … it will produce STANDING (PROBABILITY) WAVES ! – exactly like waves on a drum, – … or on a fixed string of length L ! – but: it is probability that waves !
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PHY122_L23 - PHY122 Physics for the Life Sciences II...

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