How any EM wave travels in a vacuum or an empty space as the propagation of any wave needs a matter or disturbance. Any wave can propagate in a disturbance only. How can it travel in vaccum?  As wave's propagation needs to have any disturbance.
As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields?
Punctuations with relative pronouns Sogou is a Chinese search engine, which can search text, images, music and maps.  Is a comma required before "which" in the above sentence? Stop execution of Javascript function (client side) or tweak it In which order should I play the Borderlands series? can you explain me the working of this circuit in detail? this circuit is a occupancy light circuit i want to know the working of the transistor regarding base,collector and emitter in the transitor Negative pressure How is negative pressure created in a fluid system?Isn't it counter intuitive that we are reducing the pressure of a system containing no molecules(zero pressure) to a lower value? When would you call java's thread.run() instead of thread.start()? When would you call Java's thread.run() instead of thread.start()? Is it safe to delete the file Caches, in the Library of the Mac OS X Hard Drive?  It's a pretty big file, 3.56 GB, Caches reminds me of logs i don't need or browser cookies.   Is it safe to delete the folder "Caches"? My network icon is always a question mark but I have acces to internet Gauss law question with regard to this example I am really confused in Gauss law.  Why do E3 and E2 pointing up? and also E1 pointing down?  The lecture note said infer from symmetry and you will get the following but I dont really understand. Could anyone explain to me? I am new to gauss law. How do I delete all Folders with a specific name (e.g. 128Kbps_Songs) without deleting its files  For example if I have directory "MP3_SONGS" with subdirectories "A", "B", "C" and each subdirectory has MANY directory Contains Film Name "FILM_NAME1", "FILM_NAME2", "FILM_NAME3" in it, In That Each Film NAme I have specific Folder NAme (128Kbps_Songs) in this "128Kbps_Songs" Folder I have That Film mp3 Songs Files  how can I remove the Folder "128Kbps_Songs", in Each Film_Name directory and Have to get these mp3 songs in that FILM_NAME..   ( Have to Delete 128Kbps_Songs Folder in all FILM_NAME without deleting the mp3 Songs in it, have to get the mp3 in FILM_NAME Directory..  MP3_SONGS (Parent Directory) ------ A , B, C  A (Sub Directory1) ------ FILM_NAME1 , FILM_NAME2 B (Sub Directory2) ------ FILM_NAME3 , FILM_NAME4 c (Sub Directory3) ------ FILM_NAME5 , FILM_NAME6  FILM_NAME1 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME1 (MP3 Files) FILM_NAME2 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME2 (MP3 Files)  FILM_NAME3 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME3 (MP3 Files) FILM_NAME4 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME4 (MP3 Files)  FILM_NAME5 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME5 (MP3 Files) FILM_NAME6 (Directory) ---- 128Kbps_Songs (Directory) ------ FILM_NAME6 (MP3 Files)  Need Files in: FILM_NAME1 (Directory)  ------ FILM_NAME1 (MP3 Files) FILM_NAME2 (Directory)  ------ FILM_NAME2 (MP3 Files)  FILM_NAME3 (Directory)  ------ FILM_NAME3 (MP3 Files) FILM_NAME4 (Directory)  ------ FILM_NAME4 (MP3 Files)  FILM_NAME5 (Directory)  ------ FILM_NAME5 (MP3 Files) FILM_NAME6 (Directory)  ------ FILM_NAME6 (MP3 Files) I'm not a git master, but I have been working with it for some time now, with several different projects.  In each project, I always git clone [repository] and from that point, can always git pull, so long as I don't have outstanding changes, of course.  Recently, I had to revert to a previous branch, and did so with git checkout 4f82a29.  When I was again ready to pull, I found that I had to set my branch back to master.  Now, I can not pull using a straight git pull but instead, have to specify git pull origin master, which is annoying, and indicates to me that I don't fully understand what is going on.  What has changed which does not allow me to do a straight git pull without specifying origin master, and how to I change it back?  UPDATE:  -bash-3.1$ cat config [core]     repositoryformatversion = 0     filemode = true     bare = false     logallrefupdates = true [branch "master"] [remote "origin"]     url = git@github.com:user/project.git     fetch = refs/heads/*:refs/remotes/origin/*   UPDATE 2: To be clear, I understand that my original method may have been incorrect, but I need to fix this repo so that I can simply use git pull again.  Currently, git pull results in:  -bash-3.1$ git pull You asked me to pull without telling me which branch you want to merge with, and 'branch.master.merge' in your configuration file does not tell me either.  Please name which branch you want to merge on the command line and try again (e.g. 'git pull  '). See git-pull(1) for details on the refspec.  If you often merge with the same branch, you may want to configure the following variables in your configuration file:      branch.master.remote =      branch.master.merge =      remote..url =      remote..fetch =   See git-config(1) for details.   I can tell git pull which branch to merge, and it works correctly, but git pull does not work as it did originally before my git checkout. Formatting should not count towards the character limit on comments This is a minor frustration, but I have a  that I put italics and bold into (using asterisks.)  Now I know I just just be happy that I could do it at all, but it seems to me that those should not count toward my comment char limit. On citing "common knowledge" statements I am an undergraduate student with no experience at all.  If you are writing a research paper, that you are planning to submit for publication, how do you state that a particular statement/fact is commonly known to all and it's dicoverer/inventor is not known, and that there exists no research paper that introduced the concept but there do exist various books/websites that discuss the very concepts and a few derivatives of the concept?  I am not able to cite a particular statement/bunch of statements as I am not able to find any research paper related to that at all.  The particular thing in question is:   What should I do? I plan to self-study linear algebra this summer. I am sorta already familiar with vectors, vector spaces and subspaces and I am really interested in everything about matrices (diagonalization, ...), linear maps and their matrix representation and eigenvectors and eigenvalues. I am looking for a book that handles every of the aforementioned topics in details. I also want to build a solid basis of the mathematical way of thinking to get ready to an exciting abstract algebra next semester, so my main aim is to work on proofs for somehow hard problems. I got Lang's "Intro. to Linear Algebra" and it is too easy, superficial.  Can you advise me a good book for all of the above? Please take into consideration that it is for self-study, so that it' gotta work on its own. Thanks. The use of nominative "whom" (as in “persons whom it is foreseeable are likely to...”) How do I draw shapes inside a tikz node? I know how to draw different shapes using tikz, like this:  \documentclass{minimal} \usepackage{tikz} \begin{document}  \begin{tikzpicture} \draw (0,0) ellipse (1 and 1.5)       (0,2.5) circle (1)       (2.5,0) circle (1.5); \end{tikzpicture}  \end{document}     However, I would like to put a number of different shapes together inside a node, and I couldn't yet find a simple way to do that. I will make a little figure to include in a large diagram which is already made of several nodes.  If this is not possible, or not easy, then how do I include a JPG or EPS file in a node?  Thank you! Find the remainder when $45!$ is divided by $47$? Find the remainder when $45!$ is divided by $47$?  My approach I am using Wilson's theorem to solve the problem. I reduced the expression into ($47$-$1$-$1$)!/$47!$=$(47$-$1$)/$47$!-$1$/$47!$=-$1$-$1$=-$2$  Am I right in my approach.Please correct me if I am wrong? Please correct me how to approach towards the problem. Prove $P(x,y)$: If $x$ and $y$ are odd integers, then the product  $xy$ must also be odd.   I need a direct proof of this.  I know that $ x $ and $y$ both have to equal to $2n+1$ in order for them to be odd. But that's all I have. Any help will be appreciated. How to get around a problem with \usetikzlibrary{babel}? I am currently working on an update of tkz-euclide and new documentation but I just met the following problem. If I compile this code with pdflatex or lualatex and pgf 2.1 (The library babel does not exist with pgf 2.1) then the code compiles fine but with 3.0 pgf I must comment on the call \usetikzlibrary{babel} (pgf doc gives so I recommend to always load this library by saying \usetikzlibrary{babel}).  I'd like to know where the error occurred. Especially I would like to work around this problem.   With \usetikzlibrary{babel} I get the error Latex Error: ./untitled 2.tex:46 Undefined control sequence. l.1 \tkz@line@start  Bug in babel, bug in tikzlibrary{babel} bug in my code. I would like to keep  \usetikzlibrary{babel} but to avoid the error.  %!TEX TS-program = pdflatex \documentclass[a4paper]{article} \usepackage[french]{babel} \usepackage{tikz}  \usetikzlibrary{calc} %\usetikzlibrary{babel}  \makeatletter \pgfkeys{%     tkzdrawline/.cd,     start/.code         =  {\gdef\tkz@line@start{#1}},%     end/.code           =  {\gdef\tkz@line@end{#1}},%     start style/.code   =  {\tikzset{tkzstartstyle/.style={#1}}},%     end style/.code     =  {\tikzset{tkzendstyle/.style={#1}}},%    /tkzdrawline/.unknown/.code ={\let\searchname=\pgfkeyscurrentname\pgfkeysalso{%                          \searchname/.try=#1,/tikz/\searchname/.retry=#1}}}  %&lt;--------------------------------------------------------------–&gt; %                              Draw line %&lt;--------------------------------------------------------------–&gt; \pgfkeys{tkzdrawline/.cd, start/.code       =  {\def\tkz@line@start{#1}},% end/.code         =  {\def\tkz@line@end{#1}}, start style/.code =  {\tikzset{tkzstartstyle/.style={#1}}}, end style/.code   =  {\tikzset{tkzendstyle/.style={#1}}},   /tkzdrawline/.unknown/.code   = {\let\searchname=\pgfkeyscurrentname                                  \pgfkeysalso{\searchname/.try=#1,                                 /tikz/\searchname/.retry=#1}}}%         %&lt;--------------------------------------------------------------–&gt;  \def\tkzDrawLine{\pgfutil@ifnextchar[{\tkz@DrawLine}{%                                   \tkz@DrawLine[]}}%   \def\tkz@DrawLine[#1](#2,#3){%  \begingroup   \pgfkeys{tkzdrawline/.cd,start = {}, end = {}, start style={}, end style={},}   \pgfqkeys{/tkzdrawline}{#1}   \draw[ /tkzdrawline/.cd,#1] (#2) to%     node [at start,left,/tkzdrawline/.cd,tkzstartstyle] {\tkz@line@start}%     node [at end,right,/tkzdrawline/.cd,tkzendstyle] {\tkz@line@end} (#3);  \endgroup  }%   \makeatother   \begin{document}    \begin{tikzpicture}      \node (A) at (0,1) {};       \node (B) at (5,2) {};       \tkzDrawLine[end = {$\alpha$}](A,B)       \end{tikzpicture}  \end{document} How to get ASCII value of string in C# I want to get the ASCII value of characters in a string in C#.  If my string has the value "9quali52ty3", I want an array with the ASCII values of each of the 11 characters.  How can I get ASCII values in C#?