# Search results

5. ### A Unruh modes share the vacuum with Minkowski modes

I see, thanks!
6. ### A Unruh modes share the vacuum with Minkowski modes

But couldn't the left moving negative frequency modes be analytic in that half of the complex plane?
7. ### A Unruh modes share the vacuum with Minkowski modes

In Carroll "Spacetime and Geometry" I found the following explanation for why the analytically extended rindler modes share the same vacuum state as the Minkowski vacuum state: I can't quite understand why the fact that the extended modes [\tex]h_k^{(1),(2)}[\tex] are analytic and bounded on...
8. ### I Gauge in the Aharonov Bohm effect

Thanks for the answers, very enlightening!
9. ### I Gauge in the Aharonov Bohm effect

In p.385 of Griffiths QM the vector potential ##\textbf{A} = \frac{\Phi}{2\pi r}\hat{\phi}## is chosen for the region outside a long solenoid. However, couldn't we also have chosen a vector potential that is a multiple of this, namely ##\textbf{A} = \alpha \frac{\Phi}{2\pi r} \hat{\phi}## where...
10. ### I Is this system a superposition?

Thanks, very clear explanation!
11. ### I Is this system a superposition?

So the so-called act of measurement in the OP is the painting process, not the blind man somehow "measuring" the colour of the apple? This seems to make a lot more sense now.
12. ### I Is this system a superposition?

Thank you. Suppose then that instead of colouring apples i consider randomly assigning a spin to an electron (here surely quantum effects are coherent). If I don't observe the spin of the electron, then does this mean that the electron is in a definite spin state, but I just haven't performed a...
13. ### I Is this system a superposition?

Thank you. So this case would fall under "incomplete information situations" rather than superpositions as you have described?
14. ### I Is this system a superposition?

I guess my question is what makes something capable of being in a superposition, and other things not?
15. ### I Is this system a superposition?

just because an apple isn't an elementary particle doesn't mean that it can't be in a superposition right?
16. ### I Is this system a superposition?

But couldn't you apply that logic to an electron's spin as well? It's either spin up or spin down.
17. ### I Is this system a superposition?

So the wave function is not a superposition, it's just that the blind man can't perform the necessary measurements?
18. ### I Is this system a superposition?

Suppose a blind man builds a machine that paints three apples with three colors, either red, blue or green. Once the machine has done this, are the three apples in the following superposition: or is the wavefunction just one of It feels like because the man is blind, the apples should be in...
19. ### I Atom-photon interactions in the interaction picture (self answered)

that's the way I justify it XD
20. ### I Atom-photon interactions in the interaction picture (self answered)

The ##\sigma_z## is a diagonal matrix so to take its exponential we can simply take the exponential of the diagonal elements.
21. ### I Atom-photon interactions in the interaction picture (self answered)

What do you mean by pulled through?
22. ### I Atom-photon interactions in the interaction picture (self answered)

EDIT: I'M SO DUMB! I can't believe I can't multiply matrices together. Of course the result is not zero, the matrix on the left will be: $$\begin{pmatrix} 0 & e^{i\omega_at/2}\\ e^{-i\omega_at/2}&0 \end{pmatrix}$$ So i was solving problem 3 from...
23. ### Bar magnet made from smaller opposing bar magnets

Actually fridge magnets are made like this. Here's a fun experiement to do. Take two fridge magnets and try to slide one on top of the other. In one direction the movement will be smooth, in the other it will be quite "zig-zaggy" if that makes sense. This is because fridge magnets are stacks...
24. ### Griffiths 8.5: Impulse and Momentum parallel plate capacitor

So then I should not take into consideration the magnetic repulsion?

great!
26. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

also is the explanation I posted correct? I think it makes sense but you never know.
27. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

Oh, that makes much more sense...😅
28. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

For anyone interested, I believe I have found an answer to my question. It turns out that the formula I suggested: $$\tau_{left} = \tau_{0} + \textbf{R}\times \textbf{F}$$ is only correct when "left" is an inertial frame of reference. If instead we choose a point P that is accelerating, so that...
29. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

it doesn't make sense since ##\frac{d}{L}## is unitless whereas ##\frac{mv^2}{R}## has units Newtons.
30. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

the railroad is circular so the curve never ends
31. ### Man standing on a Railroad car rounding a curve -- How much weight is on each of his feet?

The solution to the problem (given by the book) is ##N_R=\frac{Mg}{2} + \frac{LMv^2}{Rd}##, so it is not a 50/50 nor a 100/0 distribution of weight.

38. ### EMF shielding using a conductor

Oh ok thanks.
39. ### EMF shielding using a conductor

One question: if initially (before turning on the AC supply) there is no magnetic field outside, and then after some instants, as we saw in my diagram, there is a net magnetic field outside, this means that there must be some net change in flux right? Perhaps the moment the AC supply is turned...
40. ### EMF shielding using a conductor

Oh, I see. So exactly because the external magnetic field is decreasing, the fact that we have an induced magnetic field keeps the change in magnetic flux approximately constant, thus shielding anything behind. EDIT: Also, could you elaborate on why this causes metals to be shiny? Sounds very...
41. ### EMF shielding using a conductor

So I've been trying to figure out how EMF shielding works. More specifically, I've seen videos where placing a metal conductor in front of a circular coil (with AC running through at radio frequencies) apparently shielded anything behind it. After searching online, I repeatedly saw Eddy...
42. ### Eddy currents in Faraday's Law Experiment

Ah that's right, the "tilt angle" also affects the magnetic flux.
43. ### Eddy currents in Faraday's Law Experiment

My explanation: A circular coil is connected to an AC supply at a frequency of 30-50 kHz (radio frequency). Therefore, an alternate current will be running through this “primary” coil, producing an alternating magnetic field. This magnetic field periodically decreases in strength, alternating...
44. ### E&M: Field of a Wire with non-uniform current

That is true... Well I guess I now trust Ampere's Law even more than before. Thanks
45. ### E&M: Field of a Wire with non-uniform current

I tried just evaluating the curl in cylindrical coordinates and found 0, as was expected. Soo was my initial reasoning using Ampere's law correct? Or was it just a coincidence?
46. ### E&M: Field of a Wire with non-uniform current

Isn't it faster to just use Ampere's Law in differential form?
47. ### E&M: Field of a Wire with non-uniform current

Since the current density is zero outside, is the curl also zero?
48. ### E&M: Field of a Wire with non-uniform current

do you mean the curl of the B field?
49. ### E&M: Field of a Wire with non-uniform current

Summary:: Not sure if my solution to a magnetostatics problem is correct [Mentor Note -- thread moved from the technical forums, so no Homework Template is shown] I was trying to solve problem 2 from...
50. ### DIY Electromagnetic Induction Experiment

So I was watching this video containing DIY experiments on electromagnetic induction . At minute 4:45, the dude pretty much creates a transformer without using an iron core. He runs 30-50 kHz AC in a coil (forming the primary circuit) and then brings another coil with its ends attached to a...