There's something fishy that I don't get clearly with the action principle of classical mechanics, and the endpoints that need to be fixed (boundary conditions). Please, take note that I'm not interested in answers with the hamiltonian, which isn't the point here. I want to stay within the Lagr...

Dear physics Stack Exchange, I asked my physics teacher why two electrons come in pairs and not push each other away as you would expect from negative charges. He said that according to the Pauli exclusion principle, there are a limited amount of states that can be occupied in certain energy leve...

To calculate the current in a closed loop of resistance R subject to a changing magnetic field which generates an emf $ \epsilon= - \frac {d(\phi)} {dt} $, we use the relation ohm's law in the form. $\epsilon=I*R$ My question is how do we use ohm's law here? Isn't ohm's law only valid in the form...