There are particles in a medium. When these particles oscillate with SHM motion, a flow is formed. That is called a wave.  But when there is no medium, there is no oscillation. That means no flow. Eventually no wave!   But electro magnetic wave is formed without any medium. How is it possible?  Again so many said,"EM waves are the oscillation of EM field. " Oscillation of particles mean "particles are getting down and up continuously". Then what does "oscillation of EM field " mean?
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?
How to get a list of current open windows/process with Java? Does any one know how do I get the current open windows or process of a local machine using Java?    What I'm trying to do is: list the current open task, windows or process open, like in  Windows Taskmanager, but using a multi-platform approach - using only Java if it's possible. How to get file extension from string in C++ Given a string "filename.conf", how to I verify the extension part?  I need a cross platform solution. Prevent Windows 10 from installing/updating a specific driver? It seems that the recent Synaptics driver update for Synaptics SMBus TouchPad on Windows 10 (build 100049) somehow doesn't see my middle-button. Uninstalling, and installing an older driver for Windows 8.1 from the HP site (my machine is HP EliteBook 8570w) restores the middle button functionality.    Few days later, the driver updates itself again, and I lose the middle-button.  I realize I'm running unsupported software, but is it possible to prevent updating this particular driver, without either disabling updates altogether or preventing other drivers from updating? Join tables from two different server Add new alias to Gmail without SMTP (forwarding-only address) I used to be able to go to Accounts and Import → Add another email address you own and add an email account that's only a forwarding address. That is, it's not a mailbox and I don't have SMTP access to it.  Gmail would send me a confirmation email to that address, I'd confirm it's mine, and done. Now it only gives me the option to add SMTP credentials.  Did they stop supporting the previous method? Is there any other way I can get that option back? I'm studying special relativity and saw the 2 postulates of Einstein. The most remarkable one for me is the universal speed of light. Einstein postulated that the speed of light in vacuum is the same for all inertial observers, regardless of the motion of the source. But what if we are accelerating and we are changing from one inertial frame to another, how will we observe the speed of light? Is it still the same? I suggest it's not? Because I alread saw a small introduction to general relativity where the light will bend in a gravitational field and therefore also when you accelerate. So does the speed of light change because it bends? Need guidance on this proof by mathematical induction. I am new to this type of math and don't know how exactly to get started.   $$ 1^3  +  2^3  +  3^3  +  \ldots  +  n^3  =  \left[\frac{n(n+1)}{2}\right]^2 $$ I just bought a new house and I'm looking to run some cables. One of the areas I would like to run it to would require drilling through a 2x10 sistered joist. Realizing that going through the joist should be a last resort, if the hole is 1/4" and in the middle of one of the joists will this weaken the integrity?  I have seen lots of articles about drilling through the depth of a joist, but very few regarding drilling vertically. It seems like to deleted too much files by rm -r and now I have the error of "the system is running a low-graphic mode" in Ubuntu and I have to work in Windows because of that.  However I can load it in recovery mode. I need to copy the files from Downloads folder to a flash drive. Downloads folder has them as I can see by ls command.   When I plug in a flash drive, there will be some messages saying that everything is ok (as I understood) and it's plugged. But when I go to /media/my_name and do ls then I don't see anything. I don't see anything in /run/media/my_name either(I'm not sure if should though).  I can't connect to the Internet for some reason. Ubuntu was installed by wubi.exe file.  How do I save the content of my Downloads folder to a flash drive? How to make this curly 'R' (ℛ)? Which package has a similar looking fancy R or does anyone know how to make one? (Note: the line underneath the R is just the notebook paper... this is from a scanned set of notes). Sum of two squares modulo p I have heard somewhere that for all primes $p$, for all $k$, there exist $x, y$ s.t. $x^2 + y^2\equiv k \pmod{p}$? I recall that the proof is very elementary, but I can't remember such a proof. How would one prove this? One way is to use Cauchy-Davenport, but I don't think that this is the simplest solution. I'm looking for best practice in dealing with scheduled SQL Server Agent jobs in SQL Server 2012 availability groups. Maybe I missed something, however at the current state I feel that SQL Server Agent is not really integrated with this great SQL2012 feature.  How can I make a scheduled SQL agent job aware of a node switch?  For example I have a job running on the primary node which loads data each hour. Now if the primary goes down, how can I activate the job on the secondary which now becomes primary?   If I schedule the job always on the secondary it fails because then the secondary is read-only. In almost all proofs I've seen of the Lorentz transformations one starts on the assumption that the required transformations are linear. I'm wondering if there is a way to prove the linearity:  Prove that any spacetime transformation $\left(y^0,y^1,y^2,y^3\right)\leftrightarrow \left(x^0,x^1,x^2,x^3\right)$ that preserves intervals, that is, such that  $$\left(dy^0\right)^2-\left(dy^1\right)^2-\left(dy^2\right)^2-\left(dy^3\right)^2=\left(dx^0\right)^2-\left(dx^1\right)^2-\left(dx^2\right)^2-\left(dx^3\right)^2$$  is linear (assuming that the origins of both coordinates coincide). That is, show that $\frac{\partial y^i}{\partial x^j}=L_j^i$ is constant throughout spacetime (that is, show that $\frac{\partial L_j^i}{\partial x^k}=0$).  Thus far all I've been able to prove is that $g_{ij}L_p^iL_q^j=g_{pq}$ (where $g_{ij}$ is the metric tensor of special relativity) and that $\frac{\partial L_j^i}{\partial x^k}=\frac{\partial L_k^i}{\partial x^j}$. Any further ideas? Why does TeX prefer an overfull box to hyphenating here? What tips and advice do you have for photographing the Aurora Borealis? Why $\sqrt{-1 \times -1} \neq \sqrt{-1}^2$? Why am I asked for a credit card number to download a free app? I  want to download free app in my iPod touch device and i have the following doubts.  Kindly resolve me doubts.   when i try to download it asks my credit card security number. since i am trying to download free app , why do i need to provide my credit card security code? Will i be debited for downloading the free app from app store?   I cant able to find any information regarding this on apple.  Please provide me some references about this from apple and please resolve my doubts.  Thanks a lot. On sites with new responsive theme, word wrap on long titles breaks in the middle of a word For sites that have the new responsive theme enabled, where the "Ask Question" button is in line with the question title on question pages, the word wrap on long titles is not working correctly.  It will break a word across two lines.  Here is an  from Personal Finance and Money:  Maximum width, left nav hidden:   Narrow width:   This is also happening on beta sites.  Here is an  on Sports:    These screenshots were all taken on Firefox, but I am seeing the same problems in Chrome and Internet Explorer.  One more example: Brackets in if condition: why am I getting syntax errors without whitespace? Why do most 2D platformers start off in the left and progress in the right direction? In almost all 2D platformers I've played, your avatar always starts off on the left side of the world, and continues on to the right. Is there something designers gain by doing this?