Kevin Zhou — USAPhO Practice D Problem 2 · Kevin Zhou #USAPhOD.2
Physics · electromagnetism
Problem
Now consider a triatomic molecule ABA, where the two bonds both have spring constant k.
Find the possible vibrational angular frequencies and sketch the associated motions.
Question A2
Consider a long cylindrical capacitor whose surfaces are concentric cylinders of radius r and r .
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The capacitor is filled with a gas which will break down if it experiences an electric field greater
than E . If the outer radius is fixed, which should the inner radius be in order to maximize the
0
voltage V to which the capacitor can be charged, without breakdown?
Question A3
An electron with kinetic energy 1MeV travels along the z-axis and collides with a positron at rest.
The particles annihilate, producing a pair of photons with equal energies. The rest mass of an
electron is m = 511keV/c2.
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