I have enough experience with electronics to design and solder working circuits. I never quite understood though why circuits must be closed for current to flow.  I alway understood electrical current as the movement of charged particles (free electrons usually in circuits), from a ‘high pressure’ region to a ‘lower pressure’ region.  But by that analogy I never could comprehend why no current flows when the - pole of one battery is connected to the + pole of another battery?  Please don’t say “because the circuit isn’t closed”. It’s exactly what I’d like to understand - on a physical level - why the circuit must be closed (especially when understanding electrical current as the flow of charged particles from high-density to low density)
In other words, why do we need to connect the battery positive to the negative to get electron flow? As far as I know, voltage difference is what drives current flow.  From what I understand, there's a surplus of negative charge (electrons) in the positive end of a battery (weird I know, but I guess they do it for mathematical reasons). Between the positive and negative ends of the battery is some kind of wall that prevents the electrons from diffusing, so they have to go the long way (through a wire to the other end of the battery) to diffuse and reach the receiver atoms/molecules.  So why not just have the surplus of electrons on one end go to ground to equalize (e.g. 5 volts to 0 volts should produce current)? Why does it have to be the other end of the battery? I'm sure there's atoms/molecules in the ground that could accept the extra electrons (receivers atoms/molecules for the donors in the battery).
parsing XML file gets UnicodeEncodeError (ElementTree) / ValueError (lxml) Sending packets captured with Wireshark Flow to get all site collections in a tenant Created a Flow by using the below REST call and stored the title and Urls in another list  /_api/web/lists/getbytitle('DO_NOT_DELETE_SPLIST_TENANTADMIN_ALL_ SITES_AGGREGATED_SITECOLLECTIONS')/items?$select=Title,SiteUrl   Here the problem is it is returning only 100 items but I have 360 site sollections.   Not sure what I am doing wrong What's the 'correct' way of registering/installing an Assembly to the GAC? How do I figure out what package something is in without resorting to Google? I often find myself wanting to install something, but I'm unsure of what package it's in. This is a very common occurrence for me:  $ make html sphinx-build -b djangohtml -d _build/doctrees   . _build/html make: sphinx-build: Command not found make: *** [html] Error 127  $ sudo apt-get install sphinx E: Unable to locate package sphinx  $ sudo apt-get install sphinx-build E: Unable to locate package sphinx-build   googles  $ sudo apt-get install python-sphinx   Is there a better way? What is the Linux equivalent to Windows' Program Files? , where a user had taken the time to look at the link on a post and realized that the post wasn't just off-topic, it was actually half-decently-disguised spam. So he flagged it as spam, and an overworked mod declined it, giving the questioner the benefit of the doubt. And we probably want mods to be giving the questioner the benefit of the doubt.  We also want to get rid of spam ASAP, and make the lives of mods easier. I'd like to suggest a feature the mod in question mused might be useful: An optional textbox where you can add a note saying why you think it's spam, so the mod can see it easily. In this case, the helpful user who went the extra mile could have written "Site linked doesn't relate at all to the question, instead solicits BitCoins" or similar.  One can leave a comment on the question, but:   People sometimes leave...unhelpful...comments on spam questions, and we don't want mods to have to take the time to read through them hoping for something useful It allows the user flagging the spam to do so and say why without calling attention to themselves publicly     Update: We may well want this for all flags, but in particular I had reason to want it for an NAA flag, so I've posted . What is "preimage resistance", and how can the lack thereof be exploited? How is this different from collision resistance, and are there any known preimage attacks that would be considered feasible? Can you not sell/destroy buildings? So I've started playing Gathering Storm, built a bunch of coal plants and now Global Warming is out of control mainly because of me. I've been trying to remove these power plants, but I haven't found any option to sell/destroy or even replace these buildings.  Is there seriously no way to do this? What is a reliable method to locate floating islands in Terraria? Proving $f(x,y,z)=\big(\frac{x}{a+x+y+z}, \frac{y}{a+x+y+z}, \frac{z}{a+x+y+z} \big)$ is injective Let $a\in \mathbb{R}$, $a\neq 0$, and $E=\{(x,y,z)\in \mathbb{R}^3:a+x+y+z\neq 0\}$ and $f:E\rightarrow \mathbb{R}^3$ defined by $$ f(x,y,z)=\big(\frac{x}{a+x+y+z}, \frac{y}{a+x+y+z}, \frac{z}{a+x+y+z} \big) $$ Show that $f$ is injective.    I've been trying to prove it directly by showing that if $f(x_1,y_1,z_1)=f(x_2,y_2,z_2)\Rightarrow$ $x_1=x_2, y_1=y_2,z_1=z_2$. But I get a system of equations which I'm find difficult to deal with. Any help would be greatly appreciated. If you multiclass a Warlock and a Sorcerer, then you have a character with both the Spellcasting and Pact Magic features.  PHB Page 101, Sorcerer, Spellcasting, Spell Slots:     You regain all expended spell slots when you finish a long rest.   PHB Page 107, Warlock, Pact Magic, Spell Slots:     You regain all expended spell slots when you finish a short or long rest.   PHB Page 165, Customization Options, Multiclassing, Class Features:     Pact Magic. If you have both the Spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the Spellcasting class feature, and you can use the spell slots you gain from the Spellcasting class feature to cast warlock spells you know.   Do the spell slots keep their previous method of recovery (sorcerer slots long rest, warlock slots any rest), or do they all act consistently as I am led to believe from the language of the multiclass section? Do they all recover only from long rests as per the sorcerer feature, or can they all be recovered with a short rest because the warlock feature says so? Why is James Bond less tech savvy in the Daniel Craig movies? Tips to extend battery life for laptops and notebooks This question is present as a matter of historical interest.  While you are encouraged to help maintain its answers, please understand that "big list" questions are not generally allowed on Ask Ubuntu and will be closed per the .   It is possible to greatly extend the usage time of a laptop or netbook running on battery by disabling various services and installing various packages.   What tricks or tips do people have for getting an extra hour or two out of their batteries? Search text within multiple pdfs and docs I got a bunch of notes written by other students, but they are from an old textbook that didn't deal with everything in the same order, so I need to search through the notes for every chapter (each individual chapter is in a different .pdf or .doc) for "trace conditioning" for example.  I used to use Google Desktop for this, I have Launchy now and I told it to search pdfs, but it only searches the titles, not the content.  Thanks for any help. I am working on the following problem from group theory:     If $G$ is a group of order $2n$, show that the number of elements of $G$ of order $2$ is odd.   That is, for some integer $k$, there are $2k+1$ elements $a$ such that $a \in G,\;\; a*a = e$, where $e$ is the identity element of $G$. Anomalous community user activity On the meta home page I noticed the  is listed as doing something, but cannot figure out what it is.  There is nothing on the  or its , but the recent activity is listed with the same timestamp. Learn QM algebraic formulations and interpretations I have a good undergrad knowledge of quantum mechanics, and I'm interesting in reading up more about interpretation and in particular things related to how QM emerges algebraically from some reasonable real world assumptions. However I want to avoid the meticulous maths style and rather read something more meant for physicists (where rigorous proofs aren't needed and things are well-behaved ;) ) I.e. I'd prefer more intuitive resources as opposed to the rigorous texts.       Can you recommend some reading to get started? During the 'Hard Answers' Thieves Guild quest, Karliah asked me to meet her at the Ragged Flagon.  However, it seems that she doesn't show up at the rendezvous point.  Where do I find her? sudo apt upgrade error 18.04 (Broken Packages)