Electric potential at earth and infinity We define potential as work done by ext. agent in moving charge from infinity to point of observation. Then how do we often take Earth to be at zero potential?  And if we can arbitrarily choose to call a reference point, how would my measurements change if I took Earth at 100 V?
Why the electric potential of Earth is zero? For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity)  Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we are setting its potential to zero.   Why Earth's potential is zero? And if it is zero, is it zero even if the potential is still zero at infinity?
Can I create a TIN from contours lines (shp) in QGIS? Displaying row/column of point in raster using QGIS? Is it possible in QGIS to display column and row index of pixel in raster?   I mean something similar to value tool. It's possible to do a array of Matrix in Matlab? How can I use a variable in the replacement side of the Perl substitution operator? I would like to do the following: $find = &quot;start (.*) end&quot;; $replace = &quot;foo \1 bar&quot;;  $var = &quot;start middle end&quot;; $var =~ s/$find/$replace/;  I would expect $var to contain &quot;foo middle bar&quot;, but it does not work. Neither does: $replace = 'foo \1 bar';  Somehow I am missing something regarding the escaping. When to use IMG vs. CSS background-image? In what situations is it more appropriate to use an HTML IMG tag to display an image, as opposed to a CSS background-image, and vice-versa?  Factors may include accessibility, browser support, dynamic content, or any kind of technical limits or usability principles. PSN sharing games I buy &amp; download a game from PSN on my user account on PS3 #1. Then I switch to PS3 #2 and login with the same PSN account. Can I download the same game without paying twice? Strategy for "Which is better" questions In questions that are asking:    "Which is better option A or option B?"  It seems that several close reasons immediately come to mind:   Primarily Opinion Based.  In many cases the choice between A and B is simply a personal preference, a "6 vs. half dozen", either approach will work just as well and answers to this type of question will be almost entirely opinion based. Too Broad.  In some cases A is better and in others B is better, to go through every possible use case would lead to too many possible answers or one answer that reads like a short text book. Off-topic, Minimal Understanding, include attempted solutions.  This is perhaps the the most important one. If the OP needs to know "Which is better", they should probably have tried both and decided which is better, based on a practical trial.   Yet another option would be to downvote and/or comment with a "Try it and find out".  So...  Are there cases when these questions are permissible?   Could we add some more specific guidance in the help center?  Or should we continue to handle these case by case and just downvote/close appropriately when they pop up?  Strongly related, but hopefully not a duplicate of:   "Which is faster" isn't the only case where these pop up. Will $\sum^{\infty}_{n=1}|a_n|^p$ converge? Does this email mean that I have been granted the visa? I received the following email this morning. Does it mean that my visa has been granted?  UK Visas &amp; Immigration has now assessed your UK visa application and made a decision. Your documents and the decision will be sent back to either the UK Visa Application Centre where you applied, where we will contact you by email over the next few days to collect them, or if you are using the courier return service, will be sent directly back to the address provided. Please note that TLScontact does not know the outcome of the assessment and has played no role in the decision-making process. Kind regards, TLScontact UK VIsas &amp; Immigration Difference between Inheritance and Composition Give the "some of your recent flags have been declined" banner some room The "some of your recent flags have been declined" message recently got a banner, which makes it stand out  more (which is nice) but it touches the 'Flag' button, which is less nice. Can it have some margin at the bottom (and perhaps less padding?)    Tested in the latest Safari and Firefox on macOS Catalina. Make Google stop sending 'new sign in from ...' emails I get at least two emails from Google every time I sign in to my account and I want it to stop.  I tried changing the notification settings in Gmail, but they're still coming and they're useless.  How can I stop this? Perl - Package/Module Issues Compute $\int_{0}^{\infty}\frac{x\sin 2x}{9+x^{2}} \, dx$ I have got the Client Cross Frame Scripting Attack alert in the recent CheckMarx scanner. However, it points to an auto generated ID.   I've seen the following links however, the I'm not sure about relavancy of the soluions given i.e.,          Regarding my visualforce component, I'm doing just one DML operation on a custom setting from a callout response. Also, I'm not passing any attribute to the component.   To give a background of the component, its just a list view of records from a different system retrieved through a callout on load via JavaScript.  Let me know if in case anything else is needed.   Thanks in Advance! Peace! Why are these pistons pushing? I've lately become hooked into building computers in Minecraft and today I decided to build a giant hard drive. I've built HDDs before, but not at the scale I'm currently attempting, and I anticipated problems. As I was wiring some pistons, they activated and pushed forward oddly. As far as I can tell, there's nothing powering them.    I thought at first that it might be the redstone torches (top left of above pic) but they aren't powered.   Here's a top view of the same pistons. I also thought the line of redstone above  them might be the problem (middle of above pic), but when I destroy it, the pistons stay extended.  Is there a reason why my pistons are extending? If so, is there a way to get them to power (when I want them to) without disturbing the pistons above? Mathematics Ph.D program foreign language requirement I will soon be attending a Ph.D program in mathematics. I do not know how common this practice is, but the department has a requirement that graduate students must learn a foreign language and be able to read and write mathematics in that language. The three choices are French, German, or Russian. I personally have no preference on which to learn, but I was wondering if there were other reasons that would make one language more advantageous over the others in terms of a general mathematical career. Thanks in advance in any response. conflict between hyperref and enumitem packages (and \refstepcounter) The solution outlined for each of the following two posts appears to conflict with the hyperref package.         Here is a MWE.  The desired output for the example is  1. Outer 2.1. This is line 2.1, in block 2.  2.2. Inner again 3. Outer again 4. Let’s end here   This output is indeed produced by the LaTeX source below, but if I uncomment the \usepackage{hyperref} line in the header, LaTeX gives me an error just after the \skipitem command, as described in the inline comment below:  \documentclass{article}  % \usepackage{hyperref} % if we uncomment the above line, we get an error as described below  \usepackage{enumitem}  \newlist{steps}{enumerate}{9} \setlist[steps]{itemindent=0pt} \setlist[steps,1]{label=\arabic*.,ref=\arabic*} \setlist[steps,2]{label=\arabic{stepsi}.\arabic*.,ref=\arabic{stepsi}.\arabic*}  \makeatletter \newcommand{\skipitem}{\refstepcounter{\@enumctr}} \makeatother  \begin{document} \begin{steps} \item Outer   \skipitem   % If we uncomment the \usepackage{hyperref} line in the header,   % we get the following error after the \skipitem above   %    % ./tmp.tex:20: Missing number, treated as zero.   % &lt;to be read again&gt;    %   \c@0.0ptxcii    % l.20   \skipitem   % \item[] \label{blockA}   \label{blockA}\item[]   \begin{steps}   \item\label{lineB} This is line~\ref{lineB}, in block~\ref{blockA}.   \item Inner again   \end{steps} \item Outer again \item Let's end here \end{steps}  \end{document}   Can someone help me work around this conflict, so I can use hyperref with this use of enumitems and refstepcounter?  Thanks.  (Note: smaller working examples are possible, but they give different error messages.  I'm hoping to get the current example working.) Is Unit Testing worth the effort? I am working to integrate unit testing into the development process on the team I work on and there are some sceptics. What are some good ways to convince the sceptical developers on the team of the value of Unit Testing? In my specific case we would be adding Unit Tests as we add functionality or fixed bugs. Unfortunately our code base does not lend itself to easy testing. Who turned on the lightsaber? Spoilers for The Last Jedi:      Just before Snoke is slain,   he narrates Kylo Ren's thoughts/feelings (saying things like "he turns the lightsaber towards his enemy" and so on) we see the Skywalker lightsaber being manipulated through the Force to point towards and then slay Snoke. My question is, do we know for sure who was using to Force to use the Skywalker lightsaber in this scene?   It could have been   A) Kylo Ren was turning igniting the Skywalker lightsaber with the Force. Snoke assumed the thoughts/feelings he was sensing were directed at Rey but they weren't.   Or... B) Snoke was so preoccupied with Kylo's thoughts that he wasn't paying any attention to Rey's thoughts. Rey takes advantage of this and uses the Force to turn and ignite the Skywalker lightsaber to slay Snoke. This option is reinforced by the fact that  1) the Skywalker lightsaber then zooms into Rey's hand, not Kylo's.  2) after the ensuing scuffle, Kylo Ren reveals that he hasn't switched sides; he is still a believer in the First Order.  3) Kylo Ren even tells Hux that Rey slew Snoke.