A mirror reflects all electromagnetic waves that fall on it in the visible spectrum. How does the mechanism of reflection work? Is it because when a photon hits an electron, the electron jumps to a higher energy level and then to come back to its initial energy level, it emits a photon.  If the energy levels of an atom are quantized, how can a mirror absorb all e.m waves in the visible spectrum? Shouldn`t it absorb only specific wavelengths?
The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off in the correct direction?
How to integrate Tikz code in SW? I'd like to know how to insert Tikz code in Scientific Workplace tex file. Since SW doesn't support Tikz directly, now I just create Tikz code in another tex editor and export as pdf. Then I convert pdf to images, and import images into SW. Quotient group $G/H$ is abelian iff $[G,G] \subseteq H$ Allowing all/different file type uploads What would make a question popular with high views? I was wondering what might be making my questions less attractive to users?  I get very low views most of the time. What should be done to increase a question's popularity? How should I implement hook_menu()? Sorry for posting such a simple problem but I'm having trouble understanding this concept.  In the picture below, we have a force, $ \vec F_{app}$ acting on two objects, A and B.  Mass of block A: $ M_a = 4kg $  Mass of block B: $ M_b = 6kg$  The acceleration of the two blocks can be found using F=ma  $$ 20N = 10kg * a $$ $$ a = 2m/s^2 $$  If we find the force Fba on block B from block A we get:  $$ \vec F_{ba} = 6kg * 2m/s^2 $$ $$ \vec F_{ba} = 12N $$  What I am confused about here is why don't we say that the total force $ \vec F_{app} $ applied onto block A is also applied to block B (20N). Is the force somehow distributed into the blocks? Sum of $k$-th powers I have a query pattern that must be very common, but I don't know how to write an efficient query for it.  I want to look up the rows of a table that correspond to "the most recent date not after" the rows of another table.  I have a table, inventory say, which represents the inventory I hold on a certain day.  date       | good | quantity ------------------------------ 2013-08-09 | egg  | 5 2013-08-09 | pear | 7 2013-08-02 | egg  | 1 2013-08-02 | pear | 2   and a table, "price" say, which holds the price of a good on a given day  date       | good | price -------------------------- 2013-08-07 | egg  | 120 2013-08-06 | pear | 200 2013-08-01 | egg  | 110 2013-07-30 | pear | 220   How can I efficiently get the "most recent" price for each row of the inventory table, i.e.  date       | pricing date | good | quantity | price ---------------------------------------------------- 2013-08-09 | 2013-08-07   | egg  | 5        | 120 2013-08-09 | 2013-08-06   | pear | 7        | 200 2013-08-02 | 2013-08-01   | egg  | 1        | 110 2013-08-02 | 2013-07-30   | pear | 2        | 220   I know one way of doing this:  select inventory.date, max(price.date) as pricing_date, good from inventory, price where inventory.date &gt;= price.date and inventory.good = price.good group by inventory.date, good   and then join this query again to inventory. For large tables even doing the first query (without joining again to inventory) is very slow.  However, the same problem is quickly solved if I simply use my programming language to issue one max(price.date) ... where price.date &lt;= date_of_interest ... order by price.date desc limit 1 query for each date_of_interest from the inventory table, so I know there is no computational impediment.  I would, however, prefer to solve the whole problem with a single SQL query, because it would allow me to do further SQL processing on the result of the query.  Is there a standard way to do this efficiently? It feels like it must come up often and that there should be a way to write a fast query for it.  I'm using Postgres, but an SQL-generic answer would be appreciated. What are the requirements to use iMac screen as a second monitor - Target Display Mode? I have a Surface Pro 4 and an iMac (late 2019). I would like to connect my Surface Pro to the iMac to use the iMac screen as a second monitor.  Is that possible?  What are the requirements to use an iMac as a second screen? How can I completely disable internal Mic and Webcam I want to disable the internal Microphone on my laptop and the internal Webcam completely that they're no longer selectable, and no longer available?  I will only use my external Webcam, and my external (USB) headset.  The internal audio should still be available for playback. Disable automatic driver update for only one device in Windows 10 Is there a way we can disable automatic driver update for a specific device in Windows 10? The updated driver for that device (Intel Management Engine Interface 11.x in particular) causes problems on some laptops during. The version 9.x works perfect.  I don't want to disable automatic driver installation for all devices. Selecting a database in mysql with spaces in its name I want to select my particular database in mysql console, but the problem is that my database name has a space in between and mysql ignores the part after the space. For instance, when i give the command:  use 'student registration'   I get the message:  cannot find database 'student' Can Mage Hand be used in combat to grab something from an opponent?  For example, one could grab a bow out of their hands or the arrows from a quiver, or try to push them out of a tree, etc.  Mage Hand can carry up to 10 pounds, but what is its ability to interact in situations like these? Assuming I'm paying long term capital gains tax, what is the break even point where it is more worthwhile to switch from one fund to another?  For (a hypothetical) example, if I have a fund with an expected return of 3.5%, what would be the minimum expected return of another fund to make it worthwhile to pay the capital gains tax and switch to the other fund?  (I'm assuming the answer to this question is an equation involving investment horizon, capital gains tax rate, and my current taxable gains) How can I close a terminal without killing its children (without running `screen` first)? Date Not Saving in Mysql from Php Registration Form how many terms will there be once you collect terms with equal monomials? What is the sum of all the coefficients? If you expand $(x_1+x_2+\cdots+x_k)^n$, how many terms will there be once you collect terms with equal monomials? What is the sum of all the coefficients?  I'm kind of lost here. This came up with other questions on the topic of binomial coefficients, and i have figured those out. I have spent almost an hour trying to figure where to start and haven't made any progress. Term or phrase describing action occuring when not watching I am an IT professional. More specifically in automation. I am looking for a term or phrase that describes the event when either:  a. you are watching something closely and the issue doesn't occur  or  b. you are not watching something at all and the issue does occur This girl that I'm friends with and have actually seen in person before, keeps posting [on social media] that she "loves when the transfer goes through" and gets $2000-$6000 for free quite often. She said you can make up to $6500 a day. She is not very smart and barely spells correctly. She keeps saying that all she is doing is "transfers" and that's it. So many of my friends are feeding into this crap. So I asked her what it is. She basically said "it's legit" and asked me for my bank username and password so she could see how much money to deposit into my account. I said no way and left it at that. She also said she is not stealing or doing anything illegal. She is getting her friends free money and I think they're naive. What is she actually doing? Is it illegal? I am sure she is incapable of doing crazy money wiring to different countries.   Thank you everyone for answering my question. I am not stupid, I did not give her my information. I knew she was up to something illegal, so thank you for giving me some input on what exactly she is doing. I submitted an anonymous tip to my local sheriff's department. I'm hoping they see it and pursue it, or forward it to the right authorities I.e the FBI or something. Using one group separator for integer part and another for decimal part (siunitx) I thought I was able to do something like this before, but I can't find my solution.  I would like to format my large numbers as follows:   12,504.3124 2359 3   I know I can use siunitx to partially set this up, but I'm not getting the results I want:  \documentclass{article} \usepackage{siunitx}  \newcommand\aenumA[1][4]{%%   \num[group-separator={,},        group-digits=integer,        ]}  \newcommand\aenumB[1][4]{%%   \num[group-digits=decimal,        ]}  \pagestyle{empty} \begin{document}    \aenumA{12504.312423593}    \aenumB{12504.312423593}  \end{document}   I would like a hybrid solution (commas in the integer part and spaces in the decimal).  I would actually also like to be able to group differently between the two: every three digits in the integer part, every four digits in the decimal part.  Is there a straight-forward way to do this with siunitx?  Or, do I need to split the number at the decimal and treat the two parts separately and then glue them back together?