Regarding the thread:

Method of image charges

My question is considered off topic and was put on hold. Why?

Probably it seems like "fix my homework", but:

  1. I invested quite an effort, including a descriptive image which I created.
  2. I asked regarding a specific physics concept which is normally solved with the Method of image charges. So, in contrast to most students, who simply hear a proof and nod for agreement - I tried to prove it - to actually show that it works! How on earth that could be bad for this site? I didn't need to do this for the homework - I simply wanted to see how the proof works.
    Really, don't you think you're overreacting?
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    $\begingroup$ The community has agreed that "check my mistake" questions are off-topic. So it's not over-reacting, it's acting appropriately. $\endgroup$ – Kyle Kanos Jun 17 '15 at 14:49
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    $\begingroup$ @KyleKanos If I would have written "What is the proof for the method of image charges?", would it be better? I'm supplying most of the proof! If I'd ask and answer my own question (as a wiki resource), would it be better? $\endgroup$ – Dor Jun 17 '15 at 15:21
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    $\begingroup$ That might fall under the please explicitly derive this equation/law for me which is also considered off-topic. $\endgroup$ – Kyle Kanos Jun 17 '15 at 15:23
  • $\begingroup$ @KyleKanos So I can ask "Please explain why method of image charges makes sense?", which is on topic as written by "Jims Bond" and supported by 47 upvotes. $\endgroup$ – Dor Jun 17 '15 at 15:26
  • $\begingroup$ If you can phrase your question that way, sure. $\endgroup$ – Kyle Kanos Jun 17 '15 at 15:29
  • $\begingroup$ @KyleKanos Please check it now.. $\endgroup$ – Dor Jun 17 '15 at 15:40
  • $\begingroup$ Note that Jim's model question is focused on one aspect of a larger proof. If you are asking about the whole thing, the answer Kyle links to should still control. $\endgroup$ – dmckee --- ex-moderator kitten Jun 17 '15 at 15:49
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    $\begingroup$ I just can't do this any more. All this nitpicking... Thank you anyway... $\endgroup$ – Dor Jun 17 '15 at 18:36
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    $\begingroup$ Seemed like a reasonably question to me. We can (and apparently do) get too nitpicky about finding reasons not to answer questions like this when it would be quicker (and more helpful) to answer it. When does the "be nice" policy trump the "be a stickler for the homework policy"? $\endgroup$ – Floris Jun 18 '15 at 5:40
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    $\begingroup$ @Floris the two policies are rarely in conflict. If a discussion about a homework question's topicality degenerates into personal insults, then "be nice" kicks in and earns the participants a warning and deletion of comments, or perhaps a suspension. But the underlying question of whether a particular question is on topic or not is more or less independent of niceness. For any given question, there are nice ways and not-nice ways to argue that it's on topic, or off topic, as appropriate. $\endgroup$ – David Z Jun 18 '15 at 10:36
  • $\begingroup$ BTW despite the downvotes, it was good of you to post this here on meta, Dor. Downvotes indicate disagreement on meta, not necessarily a bad question - which means that the people who downvoted you probably did so because, at the time they voted, they thought your original question (on the main site) should not be reopened. $\endgroup$ – David Z Jun 18 '15 at 10:41

To explain the difference between between patching the sentence

Please explain why the method of image charges makes sense in this scenario?

onto the end of a check-my-work problem and Jim's

Please explain what this aspect of a solution/derivation means or why it makes sense

consider that the answer to every Why is the Method-of-Images-appropriate question is "Because of the uniqueness theorem for solutions to Poisson's equation."

That said there is a conceptual question that you could usefully ask here. To find it, you have have to think about what you do and don't understand about what you are trying to do.

I'm just guessing, but you seem to understand that

  • you are going to install some virtual charges on the other side of the conductor

you might understand

  • that this is to get the electric field at the conductor to have the right properties (everywhere perpendicular) while still maintaining Gauss's Law on "real" side

but you don't seem to understand

  • how to deduce the amount of the resulting surface charge without going through a lot of tedious and error-prone math.

So ask about the thing that is actually giving you trouble, already.



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