/sci/ - Science & Math » Thread #13736015

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Anonymous Sun 10 Oct 12:52:23 2021 No.13736015 View Reply Original Report

Quoted By: >>13739980 >>13740735 >>13742876

>infinite conductive sheet in xy-plane and Z=0
>Neutral, implying equal number of electrons and protons
>introduce negative charge at (0,0,a) with a > 0
>Positive charge induced everywhere on sheet
>More protons than electrons
Where did the electrons go?

Anonymous

Anonymous Mon 11 Oct 2021 01:54:01 No.13738275 Report

Quoted By:

Bump

Anonymous

Anonymous Mon 11 Oct 2021 02:35:42 No.13738353 Report

Quoted By:

>reddit leans more dem than Twitter
Grim

Anonymous

Anonymous Mon 11 Oct 2021 16:33:14 No.13739909 Report

Quoted By: >>13739920

Does nobody have an answer here? I thought there were actual physicists here. I asked my ED prof this question, and he told me he'd get back to me.. he never did.

Anonymous

Anonymous Mon 11 Oct 2021 16:38:36 No.13739920 Report

Quoted By: >>13740735

>>13739909
this is a science board
there's nothing scientific about an "infinite conducive sheet"

Anonymous

Anonymous Mon 11 Oct 2021 16:54:34 No.13739980 Report

Quoted By:

>>13736015
>mix idealizations and non-idealizations haphazardly
>act surprised when you arrive at nonsensical results
Why are you like this?

Anonymous

Anonymous Mon 11 Oct 2021 21:46:14 No.13740735 Report

Quoted By: >>13741541

>>13736015
It would get to the surface as far away as possible.

>>13739920
The Cu plane of YBCO is a pretty good approximation.

Anonymous

Anonymous Mon 11 Oct 2021 22:15:48 No.13740806 Report

Quoted By: >>13741541

Nice question, probably to maintain charge neutrality a negative charge density has to be on the other side of the (infinitesimally thin) sheet.

Anonymous

Anonymous Tue 12 Oct 2021 02:32:14 No.13741541 Report

Quoted By: >>13742073

>>13740735
>>13740806
This would imply the naive solution of a positive charge everywhere is incorrect. I believe the edges will be negatively charged, with the corners most negatively charged.

Anonymous

Anonymous Tue 12 Oct 2021 06:50:38 No.13742073 Report

Quoted By: >>13742841

>>13741541
I don't think so for the following reason: A positive charge is induced due to inluence, which means that the electrons and nuclei are shifted a little. The direction of this shift has to be in the direction of the electric field.
Consider e.g. the middle of the plate, where the angle of the electric field lines to the surface is 90°. There the positive charge is influenced by shifting the electrons and nuclei precisely perpendicular to the plate. Now since our plate is infinitesimally thin, we have a surface charge with opposite sign on the other side (in a plate with finite thickness this would be some decreasing volume charge).

Mathematically, you get it by requiring local charge neutrality, which again refelcts the fact that we are dealing with a solid where the shifts between nuclei and electrons are small.

Anonymous

Anonymous Tue 12 Oct 2021 13:31:50 No.13742841 Report

Quoted By: >>13743165

>>13742073
That would produce an oppositely signed electric field below the plate which I don't think occurs. The electric field is positive and uniform both below and above the plate, and nonuniform and tough to calculate at the edges. This would indicate the negative charges have to be at the edges.

Anonymous

Anonymous Tue 12 Oct 2021 13:43:11 No.13742860 Report

Quoted By:

you can't just 'introduce a negative charge' without creating a positive charge somewhere else.

Anonymous

Anonymous Tue 12 Oct 2021 13:55:39 No.13742876 Report

Quoted By:

>>13736015
maybe post a picture of the problem instead of a random shoycial media pic

Anonymous

Anonymous Tue 12 Oct 2021 15:49:45 No.13743165 Report

Quoted By:

>>13742841
Actually this is precisely what occurs, you calculate it via the method of mirror charges. For the easier to envision example of a conducting sphere, see e.g. https://physics.stackexchange.com/questions/411476/where-does-induced-charge-come-from-on-conducting-sphere#411514

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