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3
votes
3answers
2k views

Rotational speed of a coil in a uniform magnetic field at equilibrium

I'm looking at the following problem from "Physics 3" by Halliday, Resnick and Krane (4th edition): The armature of a motor has 97 turns each of area 190 cm² and rotates in a uniform magnetic ...
2
votes
0answers
153 views

Functional determinant approximation

Let the Hamiltonian in one dimension be $H+z$, then I would like to evaluate $\det(H+z)$. I have thought that if I know the function $Z(t) = \sum_{n>0}\exp(-tE_{n})$ I can use $$\sum_{n} ...
3
votes
2answers
137 views

Interacting classical strings?

May classical strings be interacting? I would guess no, I can not see any way to break a classical closed string in two of them (the "pants" diagram); but maybe I'm missing something.
13
votes
4answers
1k views

Tree level QFT and classical fields/particles

It is well known that scattering cross-sections computed at tree level correspond to cross-sections in the classical theory. For example the tree level cross-section for electron-electron scaterring ...