Saturday, December 31, 2016

quantum mechanics - Canonical momentum in different coordinate system


The canonical momentum is defined as


pi=L˙qi, where L is the Lagrangian.


So actually how does pi transform in one coordinate system q to another coordinate system Q ?


http://en.wikipedia.org/wiki/Hamiltonian_mechanics#Charged_particle_in_an_electromagnetic_field


When dealing with the Hamiltonian of the electromagnetic field, the derivation of pj=m˙xj+eAj on the above link is usually written as p=mv+eA


but the derivation is based on using Cartesian coordinates, does it mean that p is really a vector? If we are using another general coordinates, say, spherical coordinates, can we still have p=mv+eA ? If no, I think the form of Hamiltonian in electromagnetic field


H=(peA)22m+eϕ


will only be valid in Cartesian coordinates. In any other coordinates, H carries a different form!


Any comments are appreciated.





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