# Search results

1. ### Kirchhoff's rule for circuit with two batteries

This clears my mind, thank you

Thank you!
3. ### Kirchhoff's rule for circuit with two batteries

That's the thing that bothers me a lot. What is the physical reality that corresponds to no solution? does that mean no current anywhere or what?

5. ### Find the range of acceleration so that the drums won't fall

Well, I think there are two cases, one is for the upper bound I solved(corresponds to the top drum flying up); the other case is for the lower bound(it corresponds to the situation when the top drum is falling down, i.e. N_1 and N_2 are not enough to support the top drum.)
6. ### Find the range of acceleration so that the drums won't fall

I just fixed that, now it should be fine.
7. ### Find the range of acceleration so that the drums won't fall

Problem: Attempt: I tried to solve the range by listing out the newton's 2nd laws of each drum and from the equations of the drum 2, I get Since drum 2 must stay on the bottom drums, so it will not fly up, thus I got the upper bound of the acceleration, but I don't know if it is...
8. ### About the derivation of Lorentz gauge condition

Opps, such a silly mistake........ thank you!
9. ### About the derivation of Lorentz gauge condition

The question: Show that the Lorentz condition ∂µAµ =0 is expressed as d∗ A =0. Where A is the four-potential and * is the Hodge star, d is the exterior differentiation. In four-dimensional space, we know that the Hodge star of one-forms are the followings. 3. My attempt Since the four...
10. ### Commutator relations of field operators

That helps me a lot! Thanks! Indeed, my calculations are wrong after (3). And I also forgot that $\nabla'$ only acts on x' !!
11. ### Commutator relations of field operators

Here is the question: By using the equality (for boson) ---------------------------------------- (1) Prove that Background: Currently I'm learning things about second quantization in the book "Advanced Quantum Mechanics"(Franz Schwabl). Given the creation and annihilation operators(), define...