|MadSci Network: Physics|
According to the Heisenberg uncertainty principle, one cannot say exactly where the electron is, nor exactly how long it will take to get there, nor how long it will stay there. It is possible that an electron at the beginning energy level disappears and an electron at the ending energy level appears. (This does not violate any law of physics if it occurs in a time that is less than that predicted by the Heisenberg Uncertainty Principle) Your question is good because it DOES take a finite amount of time for the energy transition to take place. Because of the finite time required for the transition, no spectral line can be truly monochromatic. For a gas, the shape and width of a spectral line is related to the time for the electron transition, the Doppler effect and the temperature and pressure of the gas. An expression for the spectral line of a gas that only takes into account the time of the electron transition is called a Lorentz Line. It is possible to develop a theoretical expression for the Lorentz Line, or the spectral line can be analyzed experimentally. In theory, the electron transition is instantaneous, but in reality, the width of the Lorentz Line shows that it does take some finite amount of time for the transition.
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