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Quantum Theory

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Skyler Saucedo

on 12 May 2010

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Transcript of Quantum Theory

Quantum Theory Planck's Hypothesis &Blackbody radiation The Photon: Energy, Mass and Momentum Compton Effect Photon Interactions: Pair Production De Broglie Wavelengths Electron Microscopes Atomic Spectra The Bohr Model 1927 - The Copenhagen interpretation Views of Quantum Physics by are agreed upon by the founders -

universal truths emerge.. Neils Bohr and Werner Heisenberg Postulates of the Copenhagen Interpretation: 1. A system is completely described by a wave function , which represents an observer's knowledge of the system. (Heisenberg)
2. The description of nature is essentially probabilistic. The probability of an event is related to the square of the amplitude of the wave function related to it. 3. It is not possible to know the values of all of the properties of the system at the same time; those properties that are not known with precision must be described by probabilities. 4. Complementarity principle: matter exhibits a wave-particle duality. An experiment can show the particle-like properties of matter, or wave-like properties, but not both at the same time.(Niels Bohr) 5. Measuring devices are essentially classical devices, and measure classical properties such as position and momentum. How QM got it's start: Niels Bohr Danish Physicist, father of quantized atomic structure.

Worked at Los Alamos on Manhattan Project

Won Nobel prize in 1922, for proposing a new atomic model. What is Quantum Mechanics?
A set of scientific principles used to measure energy and matter at subatomic scales.

Newtonian attempts towards understanding how atoms behave

quanta - 'how much' or 'how many' QM is abstract and nonintuitive quantum corral - Fe and Cu atoms,
which is which? 5000 times smaller than a human hair, this elliptical ring of 36 cobalt atoms creats a quantum mirage.

Single cobalt atom (purple peak) is placed at one of the two foucs points of the elliptical ring, some of its properties suddenly appear at the other focus (the purple spot in the lower left), where no atoms exist. Observables: energy, position, momentum, and angular momentum.

Continuous (e.g., the position of a particle) or Discrete (e.g., the energy of an electron bound to a hydrogen atom).

No definite values to observables.

Uses probability distributions.

Probabilities will depend on the quantum state at the "instant" of the measurement. QM is the study of observables coherent electron(particle/wave) flow Why probability?

When dealing with things in the quantum world, (very small and very fast) the mere act of measuring
destroys your measurement. in Bohr's model,
orbital electrons reside in energy levels. When an electron drops into a lower energy state, it emits a photon associated with the energy difference Werner Heisenberg Won Nobel prize in 1932 for developing matrix formulations in QM

Proposed, " it is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any great degree of accuracy or certainty"

this is not a statement about the limitations of a researcher's ability to measure particular quantities of a system, but it is a statement about the nature of the system itself the photoelectric effect Wave Particle Duality Still, many physicists didn't agree with these findings the math was too complex, the ideas too abstract... Postulates of the Copenhagen Interpretation: Postulates of the Copenhagen Interpretation: Schrodinger's cat Postulates of the Copenhagen Interpretation: Postulates of the Copenhagen Interpretation: Quantum Tunneling In QM, particles exhibit a small likelihood that they can tunnel across energy barriers - A scanning tunneling microscope (STM) is a powerful instrument for imaging surfaces at the atomic level. Its development in 1981 How an STM works The STM is based on the concept of quantum tunneling. When a conducting tip is brought very near to the surface to be examined, a voltage differenceapplied between the two can allow electrons to tunnel through the vacuum between them. The resulting tunneling current is a function of tip position, applied voltage, and the local density of states (LDOS) of the sample. Information is acquired by monitoring the current as the tip's position scans across the surface, and is usually displayed in image form. STM can be a challenging technique, as it can require extremely clean and stable surfaces, sharp tips, excellent vibration control, and sophisticated electronics. Images of STM SEM The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons Samples must be prepared with a gold coating... Other SEM images
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