In photoelectric experiment, we always keep the work function constant. It seems to me that as the metal plate loses its negative charge, it may take more energy to pick up an electron off the surface of the conductor.  Is my intuition correct? And if so, does the maximum kinetic energy of photoelectrons decrease with time?
In a photoelectric effect we remove electrons from a metal using high energy photons, the work function is the minimal energy required for this effect.  My question is why doesnt the work fucntion depended on time? The more electrons we take out from the metal, the more ionized it becomes (if we remove a lot of negative charge, it will turn positive), and as a result we would expect to need more energy for this effect (the possitive charge of the metal would make it harder to remove the remaining electrons).  Why does the work function remains constant no matter how much electrons we take out?
What is the preferred way to remove spaces from a string in C++? I could loop through all the characters and build a new string, but is there a better way? After upgrading to 13.10, I am now getting a prompt for my gmail password every time I log in. There is no indication as to which service or application needs this information. If I enter the correct password I'm told it is incorrect. My gmail account does not use two factor authentication. The problem has only started after an upgrade from 13.04 to 13.10.  How can I prevent this prompt appearing, and/or what is doing the prompting? How do I print all lines of a file with duplicate values in a certain column I have just got a new laptop, It is running Windows 7 Home Premium.  I have shrunk the windows partition to give me some empty space and now I want to install ubuntu.  From Windows my partitions look like:   So now in the ubuntu live cd If I hit install and go manual the partitioner looks like   So I thought I could just select the empty space and be away laughing, but when I hit it I get JSON Parsing in Android I have installed QGIS3 from the AUR package, as well as all optional dependencies:   However, when launching, I receive the following error:  Couldn't load plugin 'processing'   ModuleNotFoundError: No module named 'osgeo'  Traceback (most recent call last):   File "/usr/share/qgis/python/qgis/utils.py", line 311, in loadPlugin     __import__(packageName)   File "/usr/share/qgis/python/qgis/utils.py", line 664, in _import     mod = _builtin_import(name, globals, locals, fromlist, level)   File "/usr/share/qgis/python/plugins/processing/__init__.py", line 28, in      from processing.tools.dataobjects import *          # NOQA   File "/usr/share/qgis/python/qgis/utils.py", line 664, in _import     mod = _builtin_import(name, globals, locals, fromlist, level)   File "/usr/share/qgis/python/plugins/processing/tools/dataobjects.py", line 51, in      from processing.algs.gdal.GdalUtils import GdalUtils   File "/usr/share/qgis/python/qgis/utils.py", line 664, in _import     mod = _builtin_import(name, globals, locals, fromlist, level)   File "/usr/share/qgis/python/plugins/processing/algs/gdal/GdalUtils.py", line 35, in      from osgeo import gdal   File "/usr/share/qgis/python/qgis/utils.py", line 664, in _import     mod = _builtin_import(name, globals, locals, fromlist, level) ModuleNotFoundError: No module named 'osgeo'   Python version: 3.6.4 (default, Jan  5 2018, 02:35:40) [GCC 7.2.1 20171224]  QGIS version: 3.0.0-Girona Girona, exported   Python Path: /usr/share/qgis/python /home/thiago/.local/share/QGIS/QGIS3/profiles/default/python /home/thiago/.local/share/QGIS/QGIS3/profiles/default/python/plugins /usr/share/qgis/python/plugins /usr/lib/python36.zip /usr/lib/python3.6 /usr/lib/python3.6/lib-dynload /usr/lib/python3.6/site-packages /home/thiago/.local/share/QGIS/QGIS3/profiles/default/python   It seems to be a path issue, but I am not sure how to solve it. Pacman shows gdal and python-gdal both as installed. I'm working on a 2nd order passive low pass filter, consisting of two passive low pass filters chained together.         &ndash; Schematic created using   Let \$ H(s) = H_1(s)H_2(s) \$ where \$ H_1(s) \$ and \$ H_2(s) \$ are the transfer functions for each separate filter stage.  Then \$ |H(s)| = |H_1(s)||H_2(s)| \$  Knowing the magnitude of a passive low pass filter,   $$|H(s)| = \dfrac1{\sqrt{ (\omega R_1C_1)^2 + 1} } \times \dfrac1{\sqrt{ (\omega R_2C_2)^2 + 1} } = \dfrac1{\sqrt{((\omega R_1C_1)^2 + 1)((\omega R_2C_2)^2 + 1)}} $$  Then trying to find the cutoff frequency:  $$ \left(\dfrac1{\sqrt{2}}\right)^2  = \dfrac1{\sqrt{((\omega R_1C_1)^2 + 1)((\omega R_2C_2)^2 + 1)}} $$ $$ 2  = \sqrt{((\omega R_1C_1)^2 + 1)((\omega R_2C_2)^2 + 1)} $$ $$ 4  = ((\omega R_1C_1)^2 + 1)((\omega R_2C_2)^2 + 1) $$ $$ 4  = (\omega R_1C_1)^2(\omega R_2C_2)^2 + (\omega R_1C_1)^2 + (\omega R_2C_2)^2 + 1 $$  And I'm stuck. Research on the web tells me \$ \omega_c = \dfrac1{\sqrt{R_1C_1R_2C_2}} \$, but I can't find why? Can anybody show my the derivation to find this? WinForms Global Exception Handling? How do I read a file into a std::string, i.e., read the whole file at once?  Text or binary mode should be specified by the caller. The solution should be standard-compliant, portable and efficient. It should not needlessly copy the string's data, and it should avoid reallocations of memory while reading the string.  One way to do this would be to stat the filesize, resize the std::string and fread() into the std::string's const_cast&lt;char*&gt;()'ed data(). This requires the std::string's data to be contiguous which is not required by the standard, but it appears to be the case for all known implementations. What is worse, if the file is read in text mode, the std::string's size may not equal the file's size.  A fully correct, standard-compliant and portable solutions could be constructed using std::ifstream's rdbuf() into a std::ostringstream and from there into a std::string. However, this could copy the string data and/or needlessly reallocate memory.    Are all relevant standard library implementations smart enough to avoid all unnecessary overhead?  Is there another way to do it?  Did I miss some hidden Boost function that already provides the desired functionality?     void slurp(std::string&amp; data, bool is_binary) How to show $(a^b)^c=a^{bc}$ for arbitrary cardinal numbers? One of the basic (and frequently used) properties of cardinal exponentiation is that $(a^b)^c=a^{bc}$.  What is the proof of this fact?  As Arturo pointed out in his comment, in computer science this is called . Differences in meaning when the verb tense changes (headlines) Do comic characters sometimes get drawn like the actor playing them? I noticed in Spider-Man's recent cameo in Captain Marvel, he appeared an awful lot like Andrew Garfield who is playing Spider-Man in the recent movie.    Irrelevant of whether it is just my imagination, do some depictions of comic characters morph to be more like an actor who plays them around the time a corresponding movie is released?  By comparison, here is Spider-Man's depiction in the Spider-Men crossover: How do I restore the sources.list file? I accidentally removed my /etc/apt/sources.list file. Is it hosted by Canonical somewhere so I can re-add it to the system? It's a bit of an emergency, so I hope someone can provide a quick answer. I've been watching a lot of pro replays ever since the SC2 beta came out, and I've noticed that almost always, when Protoss research upgrades, the shields are the last research chosen. Why is that? Seems to me that if anything, shields should be the most important upgrade, as they affect all Protoss units and buildings. How to extract the decimal part from a floating point number in C? How can we extract the decimal part of a floating point number and store the decimal part and the integer part into two separate integer variables? How do you iterate backwards through an STL list? how to install packages with apt-get on a system connected via proxy? I've got an Ubuntu 11.10 system connected via a proxy to the internet, and I would like to install packages via apt-get. When I try to do that I get this error message:  sudo apt-get install libboost-program-options-dev [...] Err http://gb.archive.ubuntu.com/ubuntu/ oneiric/main libboost1.46-dev i386 1.46.1-5ubuntu2 407  Proxy Authentication Required   Any ideas? `apt-get update` cannot find Ubuntu servers Application is "Ready to Sale" but not reflected on iTunes Store Is it possible to decompose a hermitian and unitrary matrix $A$ into the sum of the Pauli matrix Kronecker products?   For example, I have a matrix 16x16 and want it to be decomposed into something like $$A =\sum_{i,j,k,l}h_{ijkl}\sigma_i\otimes\sigma_j\otimes\sigma_k\otimes\sigma_l$$ I can't find any clear explanation how it can be done. I found only this for two-dimentional case: