When a light ray strikes an interface a part of it gets reflected, a part of it gets absorbed while another part gets refracted. Why does light reflect? Why does it refract?
Whenever light rays are entering a denser medium they bend towards the normal.  Why do rays choose the path towards the normal? Why cannot they choose the path away form the normal?
Are there naturally occurring lasers? How to install program to all user accounts in Windows? I have several accounts on my home PC. I want to install a program for all user accounts, not just the one I used to perform the installation. How do I go about doing this?  I installed a program from an admin account, but it doesn't show up in the other local accounts.  I was not able to find any documentation on how to do this.  I have Windows 8.1, if that matters. Possible Duplicate:          On Wikipedia, it says that:     Matrix representation of complex numbers   Complex numbers $z=a+ib$ can also be represented by $2\times2$ matrices that have the following form: $$\pmatrix{a&amp;-b\\b&amp;a}$$   I don't understand why they can be represented by these matrices or where these matrices come from. Where are the necessary places to be appended with % to remove unwanted spaces? I have  experience where empty spaces cause unwanted effects. It is not easy to trace the cause of these unwanted effects. In order to eliminate any doubt, I often overuse % as follows.   \usepackage% [% left=3cm, right=3cm% ]% {geometry}   or  \newcommand{\mycommand}% {% This is my command.% }   I got an extreme example that will break what Leo Liu said     In fact, only spaces which would be   output have to be removed by comment.   The following code does not produce output, but we cannot remove the % and leave a blank line between two elements of a list below.  \newpsstyle{gridstyle} { gridwidth=0.4pt, % griddots=0 }   Shortly speaking, where are the necessary places to be appended with % to remove unwanted spaces? Test Class for a Custom Controller The English alphabet has a common pronunciation. For example, the letter b is pronounced like the word bee, the letter c like the word see, and the letter i like the word aye.  Is there a formal spelling for the letter names? What TV movie had lost space cadets who piloted yellow tripod robots, and a squid bad guy? In Obi-Wan's Order 66 warning transmission why didn't he tell the surviving Jedi about the Sith, including Palpatine's true identity? If you've seen the premiere episode of Rebels, you will have seen Obi-Wan's warning message that he broadcast to Jedi throughout the galaxy in RotS. In this message he speaks cryptically &amp; warns of a "dark shadow" falling &amp; to avoid the temple &amp; await a "new hope".   Wouldn't it have been useful to inform the Jedi that their mortal enemy the Sith had returned? And specifically that Palpatine himself was a Sith? You'd assume that the majority of the Jedi who were not in the loop of the Council would be unaware of the existence of the Sith. Yoda mentions a few times that they should keep it under wraps. I think now would've been the time to reveal the truth. The more info the surviving Jedi have the better. Who knows if the likes of Kanan knows anything about the Sith's return! I find Obi-Wan's omission of this information bizarre. I am running a critical research program on a Windows 7 PC that needs to run uninterrupted for several months. I have had to re-initialize the entire experiment several time due to unexpected restart. Windows Update is disabled, and I have removed automatic updating from all background programs that have an option for it, but I am still getting restarts at random intervals that completely destroy my experiment.   Is there some way to prevent any and all restart requests? Why is the ##UserID## parameter not populated in Data Explorer anymore? Environment I'm logging in using the OpenID from  and using Chrome 31.0.1650.57 m if that matters. Steps to reproduce: Log in to  and , for example, like: DECLARE @MyUserID INT = ##UserID:int##  SELECT TOP 1     Id AS [Post Link],     Score AS [Score],     CreationDate AS [Creation Date] FROM     Posts WHERE     OwnerUserId = @MyUserID AND     PostTypeId IN (2, 3) ORDER BY     CreationDate DESC  Then press the Run Query button and see if the UserID field is filled with your own user ID like shown in the below screenshot:  Question: Did something changed on the ##UserID## parameter (for example, that it's not supported anymore)?  If so, then there is an outdated  paragraph about it (What's the point of logging in). If not, it is a bug which is there about three days (I've been waiting since I noticed that you were going to do some changes to Data Explorer, but it remains there, hence my question). Is there an official Marvel Cinematic Universe viewing order? How to iterate over a comma separated list? How can I recover from deleting the /usr/share/themes directory? to infinitive as direct object?! (as in : I promised to get there in time.) I'm a passionate Korean English-learner, and I would like to ask you a question about grammar.   It was 3 years ago when I first started to study the to-infinitive as studying grammar with Grammar In Use series and English Grammar series by Longman, having been exposed to English for 3 years. There wasn't any mention of the author saying that the usage of the to-infinitive is as an (direct) object. And for me also, the times I have encountered sentences in which the usage of the to-infinitive, so to speak, as direct objects were used, I've read them as some kind of obligatory adverbial that shows what the verbs are about, not as objects, which means they are noun phases! 100% of Korean textbooks say the usage is as a direct object, but I doubt it. I think it's some kind of obligatory adverbial that shows what the verbs are about.    I thought it was better for me to ask Americans themselves. Do you read this usage of to-infinitive as a noun phrase or an adverbial? Managing module library dependencies with composer I've found ,  and  which are releated to my question, but no longer seem to apply since Drupal 8.1 and the deprecation of .  Also popular guides such as  appear to no longer apply as they also mention composer manager.   The other solution opposed to composer manager, alter the core composer.json file feels like too much core hacking and would probably break with every Drush update of Drupal core(?).  More specifically, I am attempting to update  from Drupal 7 to 8. I have created my composer.json file as follows:  {   "name": "drupal/views_vcards",   "description": "Allows creation of vCards using the fields provided by the Views module.",   "type": "drupal-module",   "license": "GPL-2.0+",   "homepage": "https://drupal.org/project/views_vcards",   "require": {     "maennchen/zipstream-php": "0.3.*"   } }   But if I put a composer.json file in my module folder, how do I make Drupal aware that that file is there, and how do I make sure the required zipstream-php library is downloaded?  Simply running composer update from the Drupal root does update a lot of Drupal dependencies, but it does not include the composer.json files that are in the modules folders. I also don't assume I should be calling composer install from inside all modules with dependencies.  How do I make Drupal aware of a module's dependency without using composer manager and/or hacking core?  UPDATE:  The  appears to have support a wildcard path:  {     "require": {         "wikimedia/composer-merge-plugin": "dev-master"     },     "extra": {         "merge-plugin": {             "include": [                 "composer.local.json",                 "extensions/*/composer.json" // &lt; ---- THIS LINE             ],             "require": [                 "submodule/composer.json"             ],             "recurse": true,             "replace": false,             "merge-dev": true,             "merge-extra": false         }     } }   Why doesn't core merge modules/*/composer.json, that would solve everything right?  Update 2:  THe reasoning for not supporting this is covered in  (which also has been quiet for some time now). How to copy all files of a certain type into a folder from command prompt? I want to copy all files of a certain type (like .docx, .pdf, etc) on my PC into a folder. How can I do that? I got a stomach flu or I got the stomach flu or I got stomach flu? When I googled stomach flu, there were many questions and statements like      How do you get the stomach flu?    Or     Difference between a stomach flu and food poisoning    Or      Six facts about stomach flu   When do you use the, a or nothing? And which should I use for a sentence like "I got a stomach flu from someone" ? $n$ choose $k$ where $n$ is less than $k$ context menu parent? How do I hide the System Reserved partition from the Windows Explorer?    On the above screenshot, I want to get rid of System Reserved (D:). How do I do that?  I will never need to access it from there, why would I need the entry then?  PS: I want to hide it, not delete it.