I picked up an extension cord today, and I noticed that it had a different value for its wattage and its ampage, based on whether the cord is wound around its base or not.     (I apologize that the picture is blurry. In the left box it says, ”Max current wound - 4 Amps (960 Watts),” and in the right box it says, “WARNING - Max current unwound - 13 Amps (3120 Watts).”)   Why does this make a difference? Assuming that the wire is properly insulated, shouldn’t it transfer the electricity just as efficiently wound as unwound? Is there a formula that I can use to calculate a cord’s wattage/amperage when only part of it is wound, or when all of it is wound, given its wattage/amperage when straight, how much of it is wound, and how tightly it’s wound, and maybe some other variable I can’t think of?   Obviously my question assumes that it has nothing to do with a liability concern or the like.
(Disclaimer: I've read the  and I do understand that this is bordering on off-topic since it's about consumer devices. However I hope that I've managed to make enough on-topic by asking about why it is the way it is, and what is the explanation from an electromagnetic point of view - in other words, what laws of electricity and what practical considerations have gone into these decisions).  I recently bought a power tool and in its manual I found a few peculiar safety rules. I cannot see why they would be there, although reading up more it seems that they are commonplace. My understanding of electricity is limited (just about enough to be dangerous), so I'm hoping to expand it. :)  The rules are:   Don't use an extension cord longer than 25m. Considering this is an outdoors tool, this limitation is severely restrictive. The best explanation I've seen is that longer cables would simply have too high of a resistance and the tool wouldn't be able to operate at full power. But this argument doesn't convince me. The tool is rated at 2.4kW, and it's meant to be used with 220V AC power source, which means it uses about 11 amps of current. All the extension cords I've ever come across have at least 16A limitation, so there is quite a reserve still. In addition, the power has to travel much, much further to get to my house, and even after the meter it still takes probably close to those same 25m to get to the power outlet. Why only 25m after the outlet? The resistance of the cables isn't that big, is it? Don't daisy-chain extension cords. I suspect this is a variation of the above - don't exceed 25m; every connection adds additional contact resistance; water in the outdoors connections can be a problem - in general, it just adds risk. However, apart from the water in the contacts, the rest seems to me to be practically negligible. Is there really a significant contact resistance? Assuming that the extension cords are in a good shape. Make sure that the power cord is entirely unrolled. This is another odd one. My suspicion is that it has to do with inductive resistance. But is it really that strong? Wherever I've seen people actually wanting to create an electromagnet, it's pretty much hard work. You need a lot of neat, tightly-wound loops of wire. An extension cord has a lot of insulator around it, spacing the wires pretty far apart, and the loops are very chaotic. In addition, if that was a problem, why do  exist? They're used especially when you need a very long extension cord, and you don't need to unroll them completely every time you want to use them. Solved: OK, I was off the mark. The correct answer (also a ) has to do with the wire heating up from being used close to its limits. When coiled together, the temperature can go pretty high and melt the cables. Not fun.
Why Did Anakin Skywalker Believe that Turning to the Dark Side of the Force Would Save Padmé? Just as the question asks: Why did Anakin come to believe that Padmé could be saved if he embraced the Dark side of the Force? Padmé clearly didn't believe it. Why was Anakin so driven to save Padmé through the dark side? Show a,b,c congruences when $a^2+b^2=c^2$ i would like to know how to prove that if $a^2+b^2=c^2$ then   a) $3|a$ or $3|b$  b) $5|a$ or $5|b$ or $5|c$  c) $4|a$ or $4|b$   Also that $a^2+b^2+c^2+1$ can't be divisible by 8  Thank you very much! How are dashes implemented in TeX? How does LaTeX implement the differences between the dashes?  -, --, and --- all print different dashes, but - is not an active character: it has catcode 12, the same as digits like 2. Create Trigger that updates the same table before (or after ??) the Insert I have just started using triggers and one thing that I would need to do is to create a trigger that updates the same table that's inserting the row.  TABLE:  CREATE TABLE `city` (   `city_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,   `city` varchar(50) NOT NULL,   `country_id` smallint(5) unsigned DEFAULT '0',   `country` varchar(150) DEFAULT NULL,   `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,   PRIMARY KEY (`city_id`),   KEY `idx_fk_country_id` (`country_id`),   CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE ) ENGINE=InnoDB AUTO_INCREMENT=6009 DEFAULT CHARSET=utf8;   Trigger:  DELIMITER $$ CREATE TRIGGER `populate_country_id` BEFORE INSERT ON `city` FOR EACH ROW BEGIN  IF NEW.country_id = 0  THEN     UPDATE city     INNER JOIN country B ON city.country = B.country     SET NEW.country_id = B.country_id;  END IF;  END $$ DELIMITER ;   MySQL is just returning: Can't update table 'city' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.  Is there any way I can make this work?  Thanks everyone! In 10.04, I had a lot of keyboard shortcuts defined using Super/Mod4 and one single other key,   Super+O ran Opera Super+W opened Nautilus pointing to my Work folder, etc.   In 11.04, these do not seem to work -- only Super+R works to run the terminal, and Super+Shift+W successfully runs Nautilus.  Is there some way I can get these to function again?  Adding them in Keyboard Shortcuts does not work, and neither does adding commands in CompizConfig Settings Manager. Convert timestamps with offset to datetime obj using strptime What does the exclamation mark do before the function? This is problem 31b) from Dummit and Foote chapter 14.2. I am looking for a hint on how to attack the problem, since I have been thinking about it for a couple of hours but I don't even know where to start. The problem says:  Let $K$ be a finite extension of $F$ of degree $n$. Let $\alpha$ be an element of $K$. Prove that the minimal polynomial for $\alpha$ over $F$ is the same as the minimal polynomial for the linear transformation $T_{\alpha}$. In this problem, $T_{\alpha}$ is an $F$-linear transformation of $K$ that arises from $\alpha$ acting by left multiplication on $K$.  I appreciate any helpful suggestions on how to start attacking the problem or any possible hint. Thanks! How do I install make? This question is prompted by:  and .  Basically, some diamond moderators don't always want to diamond-hammer close questions.  A workaround is to create a new account, , then cast regular close votes from that account.  Question: May a diamond moderator utilize a second, non-diamond account e.g. to cast regular close votes?     It is not a problem to have multiple accounts, as long as they aren't voting for each other and doing other sockpuppet-y things.      I worry this might be considered "sockpuppet-y".  The diamond close hammer is sometimes excessive, particularly  where moderators are . The symmetric cryptosystem one-time pad (OTP) seems to be very beautiful since it is perfectly secret according to Shannon. Many books, however, point out the main drawback: one must create a secret key the same length as the plaintext. For this reason, the concept of perfect secrecy has these days been abandoned, and we prefer other cryptosystems.   Now, for example, suppose I want to encode my text message with the ASCII scheme, and moreover suppose that this plaintext is 10 gigabytes long, therefore (using an OTP) the key must be the same length, 10 gigabytes. I think, however, this is a ''sustainable price'' because I'm sure that the ciphertext can't be attacked.  Practically, I don't understand why having such long keys with an OTP is a big disadvantage if we reach "the dream"-- namely, perfect secrecy. Nowadays the storage of information is very easy, so what is the real problem? I can, for example, share the "long key" in person. Can I do anything about a Nikon d750 taking 5 minutes to power on after taking saltwater damage? I have had a Nikon d750 for a year or so, and 6 months ago it took on a bit of saltwater damage. It still works, but twice in the past it wouldn't power on, once for two weeks and once for two days.   Now it is at a point where it takes around 5 minutes to power on, and when i switch the camera to 'off' or standby, it completely powers off as if the battery drops out, then it takes another 5 mins or so for it to power back on, if it does at all. So I have switched the standby timer in the settings to 'infinity' so it just stays powered on.  I am taking it in to have it looked at, I just hope the damage isn't too fatal. I wonder if anyone has experienced anything similar to this, or can help me diagnose the actual problem. I have tried different batteries, and everything else possible really. Camera itself works fine, just power issues.  thanks in advance. Prove that $\sum_{k=1}^{n}k\binom{n}{k}=n\cdot2^{n-1}$ I want to prove the following: $$\sum_{k=1}^{n}k\binom{n}{k}=n\cdot2^{n-1}$$ what I did is(use binominal): $$\binom{n}{k}X^k\cdot 1^{n-k} = (X+1)^n$$ $$k\binom{n}{k}X^k\cdot 1^{n-k} = k(X+1)^k-1$$ now I replace $k$ by $n$ and insert $X=1$ , I will get now $n\cdot2^{n-1}$ what you are suggesting? there is another way to do that? thanks! What is the maximum number of downvotes a question can have I was just wondering what the maximum number of down votes a question can have before it is removed from StackOverflow. Delay jquery hover event? I would like to delay a hover event in jquery.  I am reading from a file when user hovers over a link or label.  I don't want this event to occur immediately in case the user is just moving the mouse across the screen.  Is there a way to delay the event from firing?  Thank you.  Example code:  $(function() {     $('#container a').hover(function() {         $('&lt;div id="fileinfo" /&gt;').load('ReadTextFileX.aspx',             {filename:'file.txt'},             function() {                 $(this).appendTo('#info');             }          );     },         function() { $('#info').remove(); }     }); });   UPDATE: (1/14/09) After adding the HoverIntent plugin the above code was changed to the following to implement it.  Very simple to implement.  $(function() {     hiConfig = {         sensitivity: 3, // number = sensitivity threshold (must be 1 or higher)         interval: 200, // number = milliseconds for onMouseOver polling interval         timeout: 200, // number = milliseconds delay before onMouseOut         over: function() {             $('&lt;div id="fileinfo" /&gt;').load('ReadTextFileX.aspx', {filename:'file.txt'},                 function() {                    $(this).appendTo('#info');                 }              );         }, // function = onMouseOver callback (REQUIRED)         out: function() { $('#info').remove();  } // function = onMouseOut callback (REQUIRED)     }     $('#container a').hoverIntent(hiConfig) } Consider these two sentences: "I gave him a pencil," and, "I gave a pencil to him."  Is it correct that the important part of the sentence is placed at the end? When we want to emphasize the pencil that I gave him, must we say, "I gave him a pencil?" When we want to emphasize that it is him to whom I gave a pencil, must we say, "I gave a pencil to him?" New "[tag:" syntax interferes with Markdown links Badge symbol in notification is of the site you're on, not where badge was earned I have a spawn area I am hoping to make a safe haven, so I have a command block on a clock that kills each hostile mob type. This works to keep the place free of any hostile mobs, however every night I see rotten flesh, bones, arrows, and string everywhere.  I would like to add something to my command blocks so that they are killed without dropping loot. How can I accomplish this?  Note that I want mobs to drop loot generally elsewhere in the world, so /gamerule doMobLoot false will not do the trick for me. I'm hoping for a command that only applies to the mobs killed by the command block, and not anything else. Antivirus software is breaking SE web page? (blocking CSS and JS)?