Recent content by QuantumRose

  1. QuantumRose

    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?
  2. QuantumRose

    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.)
  3. QuantumRose

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

    I just fixed that, now it should be fine.
  4. QuantumRose

    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...
  5. QuantumRose

    About the derivation of Lorentz gauge condition

    Opps, such a silly mistake........ thank you!
  6. QuantumRose

    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...
  7. QuantumRose

    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' !!
  8. QuantumRose

    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...
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