I am not able to understand why the PN junction does not conduct when reverse biased. Can't electrons travel from the N side through the power supply to the P side where they can jump from one hole to other to traverse the P side and then cross the depletion layer back in to the N region ?
Consider this reverse biased diode :     I read that no or very small current flows in reverse biased diode as depletion layers get widened and huge resistance is offered so no electrons can cross it. But, why the electrons or holes need to cross the depletion layer? In the diagram above, the positive charges (holes) are moving towards left and the current due to electrons is also in left, so won't the circuit be completed?
Defining my own command Should I flag obviously wrong answers as NAA? Can “due to” and “because of ” be used interchangeably? Is it fine to use due to in place of because of ? How about the other way around? Are any of these sentences ungrammatical?   He was lost because of the storm. He was lost due to the storm. He lost his way due to the storm. He  lost his way because of the storm. How do I get a list of installed files from a package? If neutrinos are disfavoured as DM candidates why aren't axions? Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer ). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot account for the total dark matter abundance of the Universe. By the same token, axions are also relativistic because they have very tiny masses. Aren't they also candidates of HDM like neutrinos? Shouldn't they also be disfavoured for the same reason? dd aplied to dev USB before connect corrupt /dev/sdX and dont work I have a USB where I'm coping an ISO of 5 Mb aprox with a small OS with its own grub. If I connect the device and check it sudo fdisk -l I get:  ... Device     Boot Start   End Sectors  Size Id Type /dev/sdb1  *        1  9551    9551  4.7M cd unknown   If I copy with dd the ISO sudo dd if=my_os.iso of=/dev/sdb   14852+0 records in 14852+0 records out 7604224 bytes (7.6 MB) copied, 0.538487 s, 14.1 MB/s   It works perfectly. An boot from BIOS in other PC.  The problem is, sometime I forget to connect the USB after update the BIOS, so I do ff WITHOUT the USB connected,  the output is:  14852+0 records in 14852+0 records out 7604224 bytes (7.6 MB) copied, 0.00987684 s, 770 MB/s   Now, the /dev/sdb register is corrupted, the copy speed (770 MB/s) have no sense, and cannot user again dd until reboot.  I have tried to repair it with ddrescue and it doesn't work  sudo ddrescue /dev/zero /dev/sdb conv=noerror,sync   My question is, what is happening exactly and if is possible, how to repair /dev/sdb to avoid reboot and dd start working again?  Thanks. How can I distribute a native executable for a Python program? Prove universal morphism is unique up to unique isomorphism. I'm following along Wikipedia page() on universal property, and this seems it should be trivial, but I couldn't finish the proof.  The definition I am working with:   The problem   So I want to prove that if $(A, u)$ and $(A', u')$ are universal morphism from $X$ to $F$, then there exists unique isomorphism $k: A \rightarrow A'$ such that $u' = F(k) \circ u$.   My attempt:   For any $B \in C$ and $f: X \rightarrow F(B)$, there exists unique $h: A \rightarrow B$ such that $f = h \circ u$.  Letting $B = A'$ and $f = u'$, we see that there exists unique $k: A \rightarrow A'$ such that $Fk \circ u = u'$.  This shows existence and uniqueness. We only need that $k$ is isomorphism, but this is the part I cannot prove.   Similarly, there exists unique $k': A' \rightarrow A$ such that $Fk' \circ u' = u$.  Plugging into each equation, we get  $$Fk \circ Fk' \circ u' = F(k \circ k') \circ u' = u'$$  $$Fk' \circ Fk \circ u = F(k' \circ k) \circ u = u$$  but this of course doesn't imply $F(k \circ k') = id$, so it seems useless.   Thanks for your help! Why can't variable names start with numbers? What do wizard children do before attending Hogwarts? Most of the wand-carriers that come from a non-Muggle family seem fairly uneducated when it comes to interacting with Muggles.  This implies that they don't go to any type of Muggle school before entering into their education at Hogwarts (or whichever Wizarding school they go to), or else they would at least understand some Muggle culture.  What do children from magical families do before going to Hogwarts if they don't go to a traditional school?  Is there any evidence that they're homeschooled? An item to break only SPECIFIED blocks? I know that I can make certain blocks only placeable on a specified block, but what is the command to give an item that can only BREAK certain blocks? When should I fudge dice rolls? When I started my first D&amp;D campaign as a DM, I accidentally rolled and confirmed a crit on a PC from a goblin. It was an instant kill as our campaign had no cleric. That time I decided to fudge the dice. Now, there's a similar problem, but this time the PCs are at 3rd level and they are dealing with a very important NPC. If they fail this one diplomacy check, the entire game world will fall apart, as the king would then send his entire army against the PC's homeland and will destroy it, plunging my entire game world into chaos, at which time drow that I wanted to save for a later adventure will have to come out, which will instigate a wizard's guild to release their secret ultra-deadly virus, and everything in my game world, including the PCs, will die. So should I fudge the dice roll? When is it good to fudge it? Can't delete folder in Windows 7 What is the best indicator in finding out whether a database is utilized or accessed?  I tried index statistics and  based on I/O utilization but none seem to be a good indicator.   Problem: I have a lot of databases on a development environment and due to space issues we are trying to decommission those that are not used without actually messing with the ones that are really needed. Can someone help me figure out what this TiKZ code does? Disable mouse speed check between monitors in windows 8.1 update 1 In windows 8.1 and below, the mouse would seamlessly move through all my monitors.  However, in windows 8.1 update 1 the mouse needs to be going at a certain speed before it goes to a different monitor. How do I disable this?  A google search has turned up nothing, so I'm not sure what exactly is going on Complete induction proof that every $n > 1$ can be written as a product of primes What packages do people load by default in LaTeX? I'm getting the impression from reading the answers written by some of the real experts here that there are quite a few little packages that just tweak LaTeX2e's default behaviour a little to make it more sensible here and there.  Rather than try to pick these up one by one as I read answers to questions (and thus risk missing them), I thought I'd ask up front what LaTeX2e packages people load by default in (almost) every document.  As this is a "big list" question, I'm making it CW.  I don't know if there are standard rules across all SE/SO sites for such questions, but on MathOverflow the rule is generally: one thing (in this case, package) per answer.  I guess that if a couple of packages really do go together then it would be fine to group them.  This is perhaps a little subjective and a little close to the line, so I'll not be offended if it gets closed or voted down!  (But please explain why in the comments.)  Also see our community poll question: Can I visit other Schengen countries on a long-term Schengen visa or residency permit? I have requested for a French long term (Type D) student visa from a consulate in India. It's a national Type D visa and not a Schengen visa. My question is that can we still go to other Schengen countries on this visa? If not then can we get a Schengen visa from a consulate in France? How can I make a script run automatically after gdm login and logout? I have a setup where my users log on using ldap and it works just fine.  I want to run a script after my users login (its a script that will detect which groups they are in and map network shares accordingly), and after they logout (umounting their shares).  Both scripts are done and they work.  I want that when the user logs in the box a script runs downloading the mounting script from my server (wget i guess?) and runs it, same thing for logout.  Can it be done? I've been searching the net and had no luck so far. I've managed to make that work on shell login/logout, but my users dont even know what shell is and have no use for it :)