Above is a zener diode circuit used for voltage regulation.  In Art or Electronics textbook theres a following exercise about choosing the right zener:    Always Vz = Vout and 10mA is the zener current wanted;   so R = (Vin(max) - Vz) / 10mA = (25 - 10) / 10mA = 1.5k Ohm.  and for Pz = ( Vin(max) - Vout) / R - Iout(min) ) * Vz  Pz = ( (25 - 10) / 1.5k - 0mA ) * 10 = 100mW  But actually if we can use Pz = Vz * Iz   Pz = 10V * 10mA = 100mW  I found different answers to this question in different forums. Am I doing something wrong here?
I'm having trouble understanding the simple voltage regulator that can be built using a zener diode (from section 2.04 in the Art of Electronics).  I know that it would be better to use amplifiers, et cetera, but I'm just trying to understand how this circuit works.      I don't really understand how the circuit works, but I am guessing that when a load is applied to the output, it drains current from the source (Vin) and thus causes the voltage to drop?  How does the zener diode help to maintain the voltage and thus make this circuit act as a regulator?
I was tasked to prove that when given 2 graphs $G$ and $\bar{G}$ (complement), at least one of them is a always a connected graph.  Well, I always post my attempt at solution, but here I'm totally stuck. I tried to do raw algebraic manipulations with # of components, circuit ranks, etc, but to no avail. So I really hope someone could give me a hint on how to approach this problem. How to turn off Wireless power management permanently Problem:  If $\gcd(a, b) = 1$ and If $ab = x^2$ ,prove that $a$, $b$ must also be perfect squares; where $a$,$b$,$x$ are in the set of natural numbers  I've come to the conclusion that $a \ne b$ and $a \ne x$ and $b \ne x$ but I guess that won't really help me.. I understand that if the $\gcd$ between two numbers if $1$ then they obviously have no common divisors but where do I go from this point?  Any tips at tackling this would be great. It looks quite easy though I'm still trying to get my hand around these proofs! Any pointers in the right direction would be great.  Thank you in advance, Please make the multiple comment timer less annoying (non-resetting etc.) As a little feature to prevent comment spam, you can only enter one comment every 15 seconds. That's a very reasonable limitation, since you very rarely have a good reason to write comments that quickly. I've only seen it twice at all, I think, but both times it was extremely annoying.     Only 1 comment allowed per 15 seconds; timer reset.   The reason is that every time you hit the limit, the 15 seconds begin anew. You have no indicator that tells you when you are allowed to comment again, and if you hit enter after just 14 seconds, you're back to zero. Yesterday, I went through four cycles of not quite 15 seconds, counting in my head, before I got a myself a coffee and tried again afterwards.  I suggest that you do one or more of the following (in decreasing order):   Make the counter non-restarting Add a visible countdown Make it clearly visible that you can't comment right now You can actually increase the waiting time, if it is clearly visible and there is no unnerving invisible countdown. Actually, just remove all comment fields after one comment, and tell the user to reload the page. Just please don't have UI elements that look like they would work, but feel like they are trolling you. "On their back" or "on their backs"? After the therapy, eight children (43%) became able to crawl/move on their back.   Or should I use "on their backs"?   Singular because each child only has one back, or plural because we're dealing with eight backs? Does the speed of light vary in non-inertial frames? The speed of light is the same in all inertial frames.  Does it change from a non-inertial frame to another? Can it be zero?  If it is not constant in non-inertial frames, is it still bounded from above? These badges were only recently added to StackExchange. I would like to know if there is any way I can find out how many more questions I should ask to get these badges.   For e.g. like the counters for the review-related badges: Single-word synonym for "immensely valuable"? I am looking for some (may be rarely know to nonnative English speakers) synonyms for  "immensely valuable" or "extremely valuable". Elementary formula for permutations? Add a section before \tableofcontents to content I'm too spoiled by Windows utilities that take a digital snapshot of your entire drive, which you can then restore from in the event of a drive crash.  (e.g. like Time Machine for Mac OS X).  Is there a similar way of doing this in Linux? Any open subset of $\Bbb R$ is a countable union of disjoint open intervals Using round function in QGIS expression? Since reading the answers to my question about  I've been good about giving my meat time to defrost in the refrigerator. However, my plans for tonight have changed and I'd like to defrost some ground beef that is completely frozen for dinner this evening. What are my options to do so quickly and safely? How to parse HTML with PHP? TeXnicCenter & Adobe Acrobat 10 How permanent magnets work?Are they working with motion of electrons? Back when the first discussion about deleted questions came up, I  building an official unofficial read-only archive for good deleted SE content.  I had a plan to build something like this:    Each link would point to a 1:1 scraped StackOverflow (or other SE network) deleted question (of course with a big fat disclaimer to the top, historical data, legal stuff, yada yada yada - and of course after asking Stack Exchange for permission, seeing as this would go far beyond what the CC license allows.)   I also registered a domain name that would (IMO) suit nicely, overflown.org.  However, when thinking about it, I realized doing this properly is a lot of work. You would have to:   build a scraper that can use a 10k+er's OpenID to fetch the deleted question (using the API or the data dump is for wusses. If we go through all this trouble, we want a historical document of what the site looked like "back then", right?) edit the page's DOM to remove dynamic elements, remove the "deleted" CSS classes, remove all the voting abilities from the buttons, and add the "this is historical data" disclaimer fetch - this is the biggest part and applies even if you use the API or data dump - all linked image resources (even those from imgur - even images used only in deleted questions could be purged one day), store them, and link them fetch all associated CSS style sheets and store them intelligently - preferably in a way that you don't fetch a copy of each file for each page (as normal page scrapers do), but also in a way that doesn't break if SE update their style sheets   long story short, I won't be in a position to build this any time in the foreseeable future - with old work, new work, and studying, I really have enough on my plate already.  Of course, if somebody else in the community feels like giving this a try, cool! But what I was really thinking is - maybe this is something Stack Exchange should build after all?   I know Jeff's  on these questions is used to be     @system I did think about a sweet place for them, in the bitbucket. – Jeff Atwood♦ Dec 29 '10 at 1:54   but come on. Think about it:     Future deletion discussions and changes in on-topicness policy would become way more relaxed because the popular and loved stuff has a place to go. A site for "overflown" questions could be curated by selected community members, who decide whether a contribution deserves to be archived or not.  A separate domain name (I'm happy to donate overflown.org for the purpose if desired) and the separate site design would create enough distance to the Stack Exchange network: it would be crystal clear that this read-only archive is for historical purposes only, and the existence of a question there does not mean you can ask something similar on one of the live sites. The pages would be 1:1 scrapes of what the site looked like at the time of the scraping, making it a general historical archive as well. These questions traditionally drive a lot of traffic. The possibility of continuing to show ads in the usual places would allow Stack Exchange to take advantage of that traffic without endangering content quality on the SE network. Hosting an archive like this is a job for a business, not us regular joes. A private project hosted by some community member can go down once they forget to pay a bill, or decide they want to password protect their private blog or photo album. The ideal place to host a site like this is at a company with professional admins that intends to stay online for a long time.    How about it? How do I forward/NAT all traffic to one interface/IP to a remote IP? I have one "server A" that has multiple IPs attached to it, like so:  eth0:0 1.1.1.1 eth0:1 1.1.1.2 eth0:2 1.1.1.3   I have another "server B" that also has multiple IPs attached to it, like so:  eth0:0 2.2.2.1 eth0:1 2.2.2.2 eth0:2 2.2.2.3   Now, I want to setup iptables on "Server A" to forward/NAT all incomming traffic on "eth0:2" to IP 2.2.2.3 on "Server B".  I have verified that "Server A" is able to "talk" to "Server B" on IP 2.2.2.3. Ping and telnet to open ports works just fine and I have the forward-flag turned on (net.ipv4.ip_forward=1)  I have tried multiple different ways, DNAT, SNAT, MASQUERADE etc, but I cannot get anything to work.  This line works fine if I try to forward traffic between IPs on the SAME server:  iptables -t nat -A PREROUTING -d 1.1.1.3 -j DNAT --to-destination 1.1.1.2   But if I switch out the "1.1.1.2" for "2.2.2.3", it does not work.  I assume that I need a second iptable rule to solve it. I have tried with the following POSTROUTING rules without any luck (not at the same time):  iptables -t nat -A POSTROUTING -d 2.2.2.3 -j MASQUERADE iptables -t nat -A POSTROUTING -d 2.2.2.3 -j SNAT --to 1.1.1.3 iptables -t nat -A POSTROUTING -j MASQUERADE   What am I missing?  EDIT 1:  I finally got it to work by using the following:  net.bridge.bridge-nf-call-iptables=0  iptables -t nat -A PREROUTING -d 1.1.1.3 -j DNAT --to-destination 2.2.2.3 iptables -t nat -A POSTROUTING -d 2.2.2.3 -j SNAT --to 1.1.1.3   However, now another problem appeared. All logs etc on server 2.2.2.3 shows that ALL traffic now comes from 1.1.1.3, like apache logs, mail logs etc. I assume this is the nature of NAT.   However, when I do standard port forwarding on my home-router to my laptop that is running apache, I see the original "requester IP" in the logs. So, how does the router do this? And how can I do the same on my server setup?  Bottom line, I want to forward all traffic from Server A (1.1.1.3) to Server B (2.2.2.3), BUT I also want to be able to see where the traffic came from on Server B (2.2.2.3), i.e the apache logs should show the original IP of the requester.  I assume I should use some other way than NAT to make this happen, and it should be possible, as even my simple home-router is able to do this.  One extra thing, the IPs attached to Server A and Server B is LOCKED to each respective server. Thus, Server A is NOT able to send out traffic FROM IP 2.2.2.3. It is locked by my provider in the router. NSDate Format outputting wrong date