Where does energy come from?  If a light bulb is connected to a generator 186,000 miles away, it will take one second before the bulb lights up. (Hint: speed of light) But, electrons, the supposed carrier of current and energy, only move 23 micro-meters per second.    So, where does the energy come from that lights the bulb?  The electrons only moved 23 micro-meters.  So how did the energy get into the light bulb?  Should we redefine current flow?  Can this be answered without dragging Mr. Poynting into the discussion?  Thanks for your consideration,  Cheers,  Toby
I know that electric current is the flow of electrons but electrons have a very slow drift speed (about 2mm/s). How is it that electric current reaches its destination at almost the speed of light?
Padding a number in a filename to a fixed length I have a directory of files such as:  file.1.png file.2.png … file.10.png … file.1000.png file.1001.png …   How can I pad the number to 4 digits? It should end up like this:  file.0001.png file.0002.png … file.0010.png … file.1000.png file.1001.png … Books for particle physics and the Standard Model MySQL single table static and dynamic pivot I have a table that looks like this:  +----------------------------------------+ |Name                | kode      | jum   | +----------------------------------------+ | aman               |kode1      | 2     | | aman               |kode2      | 1     | | jhon               |kode1      | 4     | | amir               |kode2      | 4     | +--------------------+-----------+-------+   How can I make a view like this with MySQL?                      kode1    kode2     count aman                  2         1        3   jhon                  0         4        4 amir                  0         4        4 Install Alongside Windows or Something Else - Which should I use? I have old notebook with BIOS (not EFI) installed with Windows 8 RTM, want to install Ubuntu 12.10 by booting to a LiveCD.   Doing some research, I found method either to choose Something Else or Install Alongside... Which method should I use? How can I add a "C" wire to my thermostat? So, the spiffy new wi-fi thermostats want power on the C wire from thermostat, but the old thermostat doesn't have a C wire at it.  What's the easiest way to add the C wire/24 volt to the thermostat location? There is a possibility for our universe to be the surface volume of a (higher-dimensional) hyperspace. So if this possibility is true,then is there also a possibility that the other galaxies we see are our own galaxy after light has completed revolution around the three dimensional boundary (surface volume).  Know that we see different shapes for different galaxies.This can be perhaps due to other reasons like-   distance light travelled, the angle through which we look to see the other galaxy (possibly Milky Way) after     it made any number of revolutions, the part of the other galaxy (possibly Milky Way) which we see,and some other properties of light and space.   Only our Milky Way galaxy is just one possibility  Another possibilities are the number of galaxies are far less than we see because we see the same galaxy several times due to curved space.  Any possibilities for the above statements to be true? When using zero as a quantifier, is it correct to use the singular form on the object of the quantifier, or the plural form?  It sounds confusing when I put it that way, but what I mean is: Which is correct?   Your password expires in 0 days. Your password expires in 0 day.   Essentially I suppose I'm asking, does "singular" mean "one" or "the opposite of more than one", as zero is not "plural" in the traditional "more than one" sense?  I'm pretty sure "days" sounds correct, but I can't be sure. Proper submodules of Noetherian modules are intersections of indecomposable modules If $M$ is Noetherian, any submodule $N \neq M$ can be written as a finite intersection of intersection-indecomposable ones.   I just don't know how to begin with the proof of this proposition.   Very kind of you for reading or answering. Any way to have CPU temperature in the menu bar? I tried  and  but it does not update the temperature and I do not wish to change the fan speed. Can magnets rotate infinitely? There are many videos on youtube in which people arranged magnets in circle and rotated one placing in middle of that circle on a shaft, and the magnet (magnet motor) starts madly and continues its movement. Do they really rotate infinitely? If so, do they from where they get that extra energy to move so fast and infinitely?    EDIT: This question is about real world scenario  UPDATE: I am unable to find that particular video about which i talked about -- I added them to my favourites, but they are all now deleted :( -- there are hundreds of that that kind of videos. Some example videos links bash if not multiple conditions without subshell? I want to combine multiple conditions in a shell if statement, and negate the combination.  I have the following working code for a simple combination of conditions:  if [ -f file1 ] &amp;&amp; [ -f file2 ] &amp;&amp; [ -f file3 ] ; then   # do stuff with the files fi   This works fine.  If I want to negate it, I can use the following working code:  if ! ( [ -f file1 ] &amp;&amp; [ -f file2 ] &amp;&amp; [ -f file3 ] ) ; then   echo "Error: You done goofed."   exit 1 fi # do stuff with the files   This also works as expected.  However, it occurs to me that I don't know what the parentheses are actually doing there.  I want to use them just for grouping, but is it actually spawning a subshell?  (How can I tell?)  If so, is there a way to group the conditions without spawning a subshell? Use of "Or", inclusive or exclusive? My wife and I are playing a game where you roll dice and move so many spaces in a grid "vertically or horizontally".   In the use of English it is very common to say, this or the other when it comes to making a choice  (exclusive or). Now I know that "or" can also be inclusive, for example "she couldn't read or write", or can be clearly used as an xor "you either come or not" making the statement true for only one of the options but not both.   My issue is where it is not clear whether it is an inclusive/exclusive or, the best example being our game.   I argue that you can move in either direction (inclusive) and the normal use of this conjunction in English should be inclusive unless specified otherwise.   Is this right? Showing a set is closed under inverses Let $G$ be a finite group, say a group with $n$ elements, and let $\emptyset \neq S \subseteq G$. Suppose $e \in S$, and that $S$ is closed with respect to multiplication. Prove that $S$ is a subgroup of $G$.    Let $G = \{a_1, \ldots, a_n\}.$ Let $a_i \in G.$ Then any number of $a_ia_1, a_ia_2, \ldots, a_ia_n \in S,$ since $S$ is closed under multiplication. One of those $a_ia_j$ is $e$ since $e \in S.$ Then either $a_i$ or $a_j$ is $a^{-1}.$ Would this argument work? Implicit 'which is', 'which are' A new study has shown that millions of pieces of junk floating in  space could be a big hazard for satellites orbiting Earth.   Is there an implicit 'which are' in front of floating in space? Why is 'which are'  not written? Bash One Liner: copy template_*.txt to foo_*.txt? Say I have three files (template_*.txt):   template_x.txt template_y.txt template_z.txt   I want to copy them to three new files (foo_*.txt).    foo_x.txt  foo_y.txt  foo_z.txt   Is there some simple way to do that with one command, e.g.   cp --enableAwesomeness template_*.txt foo_*.txt My question is specifically for badges in a particular tag. I've heard that the rules have been changed.  How and when can one get bronze, silver and gold badges for a specific tag, say ? What are the new rules governing these badges? How unusual is getting a Masters degree in a slightly different field than Bachelors? Would it be out of the ordinary to get a Bachelors in Mechanical Engineering and then go for a Masters in something like Civil or Structural Engineering?  I don't know a lot about how transitioning to a Masters program works.. Do people usually continue on in the same field, or is branching out common? Introduce a  "general reference" close reason There is a certain amount of questions that are absolutely trivial in nature: How to format a date, how to concatenate a string, et cetera. Questions that could be solved by taking a look into the manual.  Random examples from the tags I frequent:                What those OPs need is a link to the right manual, which we should give them. But the question serves no purpose. They don't even have a use by being searchable,  because any sane search query would lead to the actual manual as the first hit.  Jeff discusses the possibility of introducing a new close reason for this over at  According to Robert's suggestion there, it could go like this:     general reference: this question is too basic; the answer is indexed in any number of general internet reference sources designed specifically to find that type of information.   Please please implement this.  Add a field (like the "enter duplicate ID here" popup) for users to suggest the correct manual link:    The suggested links would then be shown in a block in the top section of the question, like duplicate links.   Also, the amount of reputation earnable from these trivial questions is appalling. I'm sure a great portion of most high-rep users' points (including mine) is from answering "what was that function for replacing a string again?" type questions. This dilutes the value of reputation as a measure of true expertise a great deal.  I would suggest that answers to questions that get closed as "general reference" are made community wiki retroactively, taking away any reputation earned. It is known that a superconductor is a material with electrical resistance zero. My question is, it is exactly zero, a theoretical zero, or for practical realistic reasons it is effectively zero? In the last 30 years, human technology has developed massively.  Every year a new smartphone is released with a faster processor, more memory, better features.  Why hasn't the same level of progress happened in the Star Wars universe?  In The Phantom Menace, we see a number of droids - R2 units, C-3PO, Pit Droids, etc.  In Return of the Jedi - the droids we see pretty much have the same capabilities.  I would have thought that technology would still be progressing in the Star Wars universe - but it appears to have stopped.  During wars on Earth, our technology capabilities grow - so it can't just be the effect of a massive war which is causing the stagnation of development.  So, what gives?