I posted the following question several hours ago: Electric field inside sphere - Griffiths Problem 2.14. In doing so, I showed my attempt in detail and provided my thought process behind it. Within two hours (and downvotes within minutes) -- and after only one answer was posted that I felt did not answer the question -- the question was promptly closed.

I'm not asking a homework question here; I'm trying to prepare for an exam, thus the need to make sure that I'm applying concepts correctly. I also think it is unfair to lump me into the category of new users who lazily post in the style of "Here's my homework question, do it for me".

How can this question be updated so as to be reinstated? I'm trying to learn, and while the topic may seem rudimentary (a) we all start somewhere and (b) all I get told is that I'm using the wrong formula without any further explanation. How is an environment like this conducive to learning physics?

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    $\begingroup$ Related: How do I ask homework questions on Physics Stack Exchange? - "A "homework question" is any question whose value lies in helping you understand the method by which the question can be solved, rather than getting the answer itself. This includes not just questions from actual homework assignments, but also self-study problems, puzzles, etc." $\endgroup$ Commented Sep 28, 2022 at 13:12
  • $\begingroup$ @PeterMortensen That's a pretty broad category. How else, then, does learning take place without parsing these sorts of "homework questions"? By not being able to solve a homework question in absence of any arithmetical errors, it shows that one is lacking in the understanding of a method and this needs to be corrected. Every other forum I have seen values encourages discussing these sorts of dilemmas, except this one. And of course I haven't mentioned the bias towards answering the same "type" of question if it is higher level, regardless of any policy, some of which I think applies here. $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 14:38

2 Answers 2


General comments

I will first share my point of view about this particular bit:

I'm trying to learn, and while the topic may seem rudimentary (a) we all start somewhere and (b) all I get told is that I'm using the wrong formula without any further explanation. How is an environment like this conducive to learning physics?

(a) At least in my opinion, Physics SE tends to be quite aware that we all start somewhere. Most people on the site will tend to know or be interested in something about Newtonian Mechanics, but only a handful will be discussing a given very specific research topic, for example. From my point of view, most of the questions and answers in this site are exactly to help people that are starting from somewhere.

(b) While Physics SE is a website for asking Physics questions, not all questions belong here. For example, some questions are way more adequate to Mathematics SE, although they might relate to Physics in some way. For many reasons, the community of Physics SE has decided some questions are not suited to this site.

From the point of view of someone who's asking, this is usually a bummer. Fairly often I'm stuck on a problem and want to ask something here, but I know the question will get closed due to being homework-like. This is definitely quite frustrating, and I've seen many people complaining about this both on the site and in real life, when chatting with friends of mine who come in here now and then.

However, it is important to consider that this site works based on other people voluntarily answering questions for free (or for internet points hahaha). As I started staying around for a little longer and taking the time to answer other people's questions, I started noticing that I was also naturally complaining about some questions. For example, from the point of view of an answerer, it is a bummer when

  • equations are written on MS Paint instead of MathJax, making them difficult to read
  • questions that just want you to solve their homework for them
  • questions that are asking lots of different stuff in the same post and you can't answer because you only know how to address one or two points

and so on. These sorts of behavior need to be discouraged by the site to avoid it from spreading. The issue if these sorts of things become too common is that you'll eventually learn users no longer want to answer questions, and the premise of the website ends. Very often, edits are enough to correct the question and put it to a good standard. Whenever I have the time, I convert equations and texts posted as images to MathJax and leave a heads up for the author so they correct it next time. Closing a question that lacks focus has the author focus on what they are interested and perhaps separating the questions into a few more, so they become manageable.

Your question in particular doesn't have the issues I mentioned, but it does have some characteristics that do not match the site's style. In my point of view, an issue with "What did I do wrong?" is that while your question is particularly short, many aren't, and actually expect answerers to read paragraphs of calculations to find a mistake somewhere. If the site ever gets too filled with these sorts of questions, people will just stop answering. Furthermore, "Where is my mistake?" is a question that applies only to you, not to a broader community. Hence, from the point of the view of other users, these sorts of question are hardly useful. They are too specific to be found through search engines and you'll hardly end up in them to understand why this particular method works or not.

How to improve this question in particular?

My main suggestion is to get rid of "What did I do wrong?". Using Griffith's question as an example is not an issue (textbook questions are very often good starting points for deeper questions), but asking what you did wrong is sort of a red flag. As you mentioned in your post, you are confident that you did the integration right and checked it. Hence, you don't really need the details of the computation in there, nor do you need people to check what you did wrong. You already noticed that the problem seems to be in your expression of Coulomb's law (which is indeed wrong, as pointed out by the answer). Hence, isolate what you are actually concerned with and leave the details of the solution to the problem out of the question.

A structure for the question (I absolutely expect you will not copy this verbatim) could then be

I'm attempting at solving Griffiths Problem 2.14, which is [text]. I know how to do it with Gauss's Law, but when I tried using the fact that the electric field is given by [expression] I got a different answer, which led me to wonder whether that expression holds in every situation. What are the limits of applicability of this equation?

Notice this question has the following different features:

  • doesn't provide complete solutions to lazy people that might lurk on the site later;
  • the focus is no longer on checking your computations, but rather answering a conceptual question.

Of course, not everyone on the site might agree that this reformulation is adequate. Each person has a different interpretation of the site's rules and it is overall built as a community effort. In my particular understandment, this formulation would be more adequate (and it would allow for fairly interesting answers on how Coulomb's law gets adapted in Electrodynamics, for example).

  • $\begingroup$ Thank you for your response. When I asked the question I knew two things: (1) Gauss' law provides the answer (after all, the answer I compare my answer to is from the solution manual, which uses Gauss' law); (2) There is a formula for the electric field of a volume charge, of which a sphere is one. I understand that I wrote the formula incorrectly, but I explained why I don't think Griffiths' formulation is necessary in my spherical coordinate system and didn't get a response. If I get some clarity as to why the right formula solves my problem, of course I will use it. But there isn't any. $\endgroup$
    – Kman3
    Commented Oct 1, 2022 at 23:54
  • $\begingroup$ @Kman3 To get some clarity on why the right formula solves your problem, you must first explain why you think your formula was right in the first place. I just re-read your question and I couldn't really understand why you used the version you used. Clarifying this might make the post more adequate for answering as well $\endgroup$ Commented Oct 2, 2022 at 1:27
  • $\begingroup$ Another suggestion: add a reference from Griffiths for the very first equation in your post (for example, "Griffiths Eq. (X.Y) states that") so we know exactly which result you are quoting. In that way, it is easier to understand what is your difficulty right now. If that equation isn't exactly written on Griffiths (it isn't, at least not for this case), add in why you believe it to be correct $\endgroup$ Commented Oct 2, 2022 at 1:29

With due respect: it may not be an assignment question to you now but it is definitely an assignment-type question: how can it be otherwise when you quote the textbook for the statement of the problem?

I cannot see how it can be salvaged in its current form.

The answer provided is actually a very good direction to explore.

(FYI the integration you are attempting is technically non-trivial because of the $\vert \vec r-\vec r’\vert^3$ in the denominator, and a change of sign in the antiderivative between two regions.)

  • $\begingroup$ I saw the answer. In my attempt to clarify it, I was met with no response to my question and a final "go ask your professor." So I get an answer, I say I don't follow it, and then get told to ask someone else about the thinking behind another person's answer. How does that make sense, and further, how does it help me learn anything? (1/2) $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 2:41
  • $\begingroup$ It's not like my question has no relevance to physics concepts more generally: when should Gauss' law be used? Do all volume charges behave the same way? Should Gauss' law and [this formula] always give the same answer? But of course, all of these valuable insights get passed on because my question comes from a textbook. If I ask a question like "Are Gauss' law and the formula for the electric field of a volume charge compatible?" the first response will be "Of course. Do you have a situation in mind where they are not?" and then I can't mention it since it's an "assignment-type question". $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 2:46
  • $\begingroup$ @Kman3 … but this is not a site for the type of question in your original post. The issues you raise in your last comments are much more conceptual and on topic. … and I’m sorry to say if you are studying from Griffith and are not clear on when to use G’s law that’s another issue altogether: check out questions tagged as Gauss’s law. There are plenty of them around. $\endgroup$ Commented Sep 28, 2022 at 3:12
  • $\begingroup$ Firstly: I'm not unclear about when to use Gauss' law. I'm trying to experiment with different ways of solving a problem that should provide the same answer. Either I can use Gauss' law blindly for everything and then screw myself over when a distribution has no symmetry, or I can actually take the time to understand what I'm doing and become familiar with several methods at the same time. While I understand that virtually every result in classical physics is encapsulated in some theorem or another, I want to explore different methods for problem solving. Gauss' law didn't always exist. $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 4:56
  • $\begingroup$ Secondly: as I mentioned, for others to understand where I'm coming from with those bigger "issues", an example is necessary. If I ask a very broad question like "Are these two theorems incompatible?", then like I said, I will simply be told "No" and learn nothing about finer details. To me the most pedagogical value, to me and others, comes from someone discussing the flaws in my reasoning which I know run deeper than just arithmetical errors. If something like this is not fit for a "question and answer site for [...] students of physics and astronomy," then I don't know what is. $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 4:56
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    $\begingroup$ @Kman3 you’re not engaging with the core issue: as it is written now, your question is a homework-style question, and was rightly closed. I recommend you consult physics.meta.stackexchange.com/q/6093/36194 and physics.meta.stackexchange.com/q/10938/36194 . $\endgroup$ Commented Sep 28, 2022 at 10:48
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    $\begingroup$ Fine; I will delete the question. Since I've told you that it cannot be asked properly without an example, I guess the question cannot be asked at all (very in the spirit of science, I might add...). I wonder what kind of response I would receive if I question the formula for a volume charge distribution without any examples in mind... Oh well. I guess I should examine examples of good questions on this site, such as this one: it asks a Griffiths question, shows work, and asks about missing factors. Who could ask for better? $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 11:53
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    $\begingroup$ @Kman3 unfortunately for you the policy has evolved since 2012. There is genuine fear the site will be overwhelmed by “do my homework” question so the broad rule is: avoid pitching your question that way. $\endgroup$ Commented Sep 28, 2022 at 12:10
  • $\begingroup$ Ah, I see. Then I guess this thread which references it as an example of a good "homework style" question can't be edited due to an unofficial statute of limitations. You and I both know that my question was NOT pitched as a "do my homework for me" question, but alas: I guess I should follow the advice from the top answer in the thread you linked, which suggests that I should somehow know which step of my attempt is wrong before I ask which step of my attempt is wrong. $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 12:34
  • $\begingroup$ At the end of day, this whole exercise just serves as another item to add to my list of experiences with the attitudes of more learned scientists towards students of science: climb up the educational ladder and then pull it up behind you, while making sure to (a) criticise for not knowing what someone hasn't been taught and (b) encourage the blind use of formulas while lamenting about students using formulas blindly without proper critical thinking. $\endgroup$
    – Kman3
    Commented Sep 28, 2022 at 12:42
  • $\begingroup$ I'm sorry but you're missing the mark again. Imagine you are an instructor. How would you feel if your students could just "subcontract" their assignment questions to a website? $\endgroup$ Commented Oct 1, 2022 at 2:24
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    $\begingroup$ This conversation is clearly going nowhere. You are dishonestly comparing me to lazy students who expect the internet to do their work for them, despite any evidence to the contrary. I'm guessing your perspective has been tainted by said lazy students in the past, which is unfortunate. And to answer your question: if an instructor lazily scrapes standard textbook exercises for assignment problems, they should not be surprised when students lazily scrape the internet for the solutions. It is not my problem if some other teacher might have or one day use a Griffiths problem in their assignment. $\endgroup$
    – Kman3
    Commented Oct 1, 2022 at 3:16
  • $\begingroup$ With due respect: you are again missing the mark. This isn't about you, and I am not suggesting you are lazy: simply observing you are not the only user of this site, and that some are lazy. Scraping answers to homework from the internet is not a function of the source of the question: even if an instructor comes up with their own questions, a student could still post them and scape answers. This is simply more problematic for questions from widely-used textbooks. If we don't police homework questions, this site will become a free version of Chegg and all quality will be lost. $\endgroup$ Commented Oct 1, 2022 at 3:59
  • $\begingroup$ It is of course reasonable to place restrictions on the kind of questions that can be asked so that sites intended for helping well-intentioned and curious learners as a supplement to school/self-study end up being used for nefarious purposes like Chegg is (though I don't think Chegg is designed for the purposes I mentioned). However, by instituting policies as extreme as I believe Physics SE's policies to be, not only are cheaters (rightfully) punished but non-cheaters and those who simply want to gain understanding are punished as well. But alas, until then, I guess this is how it will be. $\endgroup$
    – Kman3
    Commented Oct 1, 2022 at 23:43
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    $\begingroup$ I respectfully disagree but of course you opinion is as good as mine. This is a long-standing controversial issue and if you search the PSE meta site you will see multiple points of view. The site has thrived in its current format so the community must be doing something right, however irritating the policy is to some. $\endgroup$ Commented Oct 1, 2022 at 23:52

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