Recent content by SredniVashtar
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Why Are You Still Here? A Curious Question
"Use it or lose it"- SredniVashtar
- Post #11
- Forum: Feedback and Announcements
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Electric power distribution from powerplant to homes
What you are missing is that, since the wire resistance and the load resistance (let's keep it all resistive for simplicity) are in series, they share the same current, no matter what is the power required by the load. Voltage is more or less the same at the transmitting station and at the...- SredniVashtar
- Post #5
- Forum: Electrical Engineering
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Earthed plates confusion
I believe it not to be true in general. It might be true with the unphysical case of infinite plates but the amount of charge exchanged with earth should in general be geometry dependent. I asked an artificial helper to solve a problem with three charged spheres, the middle one of which to be...- SredniVashtar
- Post #14
- Forum: Introductory Physics Homework Help
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Earthed plates confusion
The net charge of the system is not zero both before and after grounding the third plate. So I don't think you can assume the charge on the outermost surface has to be zero.- SredniVashtar
- Post #7
- Forum: Introductory Physics Homework Help
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Electronic (6v) Lamp failed - troubleshooting
The idea was that a black wire was there, soldering was inappropriate, and it detached from the pad and fell inside the body during disassembly. I saw the black wire attached to the battery pack but did not see the black wire at the bottom of the PCB. The op should probe the circuit with a...- SredniVashtar
- Post #12
- Forum: Electrical Engineering
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Electronic (6v) Lamp failed - troubleshooting
In your last photo there is a red wire attached to the BAT+ pad, but there is no wire attached to the BAT- wire. It might be needed.- SredniVashtar
- Post #7
- Forum: Electrical Engineering
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Undergrad E field in a wire
1. It is more or less an electric dipole field that decreases with distance 2. It is the value of electric field allowed by the constitutive relation in the material of the wire, that is Ohm's law in its local form. It could be very high if the conductivity of the wire is low (compatible with...- SredniVashtar
- Post #3
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
My point is that the wave is the transient, and the static field we perceive after the transient has died out is... a static field. Not a wave.- SredniVashtar
- Post #43
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
Who ever said they are in an empty universe and they are free to recombine?- SredniVashtar
- Post #42
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
Ok, let's change the timescale: instead of 20 ns, let's make it 4 billion years. We sit in the middle of this event. Would you call that perturbation that has been static for 2 billion years minus the few microseconds or milliseconds during the initial transient a "wave"? I wouldn't . I call...- SredniVashtar
- Post #39
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
Are we still talking of classical electrodynamics? Because, to my knowledge, charges are the sources of the electric field, and currents are the sources of the magnetic field. They still are the sources (in the sense of the reason for the field presence - or if you prefer it "the nonzero value...- SredniVashtar
- Post #38
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
I am seeing this from the point of view of classical ED. Fields are an expression of the presence of a charge.- SredniVashtar
- Post #35
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
That seems just semantics. But ok, the perturbation in the field between creation and annihilation is say 100 ns long and, from a distance, I have 100 feet in space where the electric field is non zero, while it is zero before and after. In the middle I only have the static electric field of the...- SredniVashtar
- Post #33
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
In the case of creation and annihilation, we can see the field itself as a change from zero field to nonzero field and then back to zero field. The argument of the field being 'already everywhere' should not apply here because the charges responsible for it were not always there. If we create...- SredniVashtar
- Post #29
- Forum: Electromagnetism
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Undergrad Coulomb's law taken to the extreme
Not only the wave, but the electric field itself would come from the charges - far far away "when" they existed. The fields propagate at a finite speed, so when I sense them - say one year later - I know some charge far away must have generated them. Then after say ten minutes, those...- SredniVashtar
- Post #23
- Forum: Electromagnetism