How to calculate required toroidal core size(Cross section area) for 200VA transformer.is that any formula or method to select core.I mean to say suppose I won't make 200VA toroidal transformer so how to select required core size OD, ID, Height of toroidal core.
Few days ago I got sample of toroidal core from my friend. I don't know any technical details of core just know OD-10cm, ID-6cm, height- 5cm and wet about 1.845 kg(M4 grade CRGO). I want to make toroidal transformer using this core but how to calculate core area and maximum VA capacity of core.I take some photos and attach.
Is there an AES identity key? The following questions are of pure theoretical nature. I don't have an application in mind.   Is there a key that makes AES the identity function? Is there a key that makes AES the identity function for certain inputs? Is it known whether such keys might exist? Are such keys known for other ciphers?   For example, I want to encrypt "Hello StackExchg" with AES with said key and the ciphertext should be again "Hello StackExchg".  When I encrypt "Hello StackExchg" with the perfect cipher one-time-pad, there is a possibility that the resulting ciphertext is again "Hello StackExchg". This possibility must exist (though it is unrealistically small), otherwise, the ciphertext would not be perfectly random but depending on the plaintext. The corresponding key for one-time-pad would be all zeros. Is it safe to use the hash of the data as the key to encrypt them? Is it safe to use the hash of the data as the key to encrypt them?  That is, if I give one some encrypted data and tell them that the key that was used to encrypt them was the hash digest of the data before encrypting, will it be easier for them to decrypt them?  Edit as I can not reply to comments: The recipient will have the keys, that is no problem. I know that this machine does not work, via thermodynamics. I am asking for an analysis in terms of mechanics and magnetism.  Anyway, so here is the machine:   (source: )    The magnet (the red ball) pull the ball up the ramp, and then it drops the ball through the hole, which then rolls down, and go ups the ramp again. Thermodynamics shows that this can not work.  From a mechanics and magnetism perspective, what happens when you do this, and why can't it happen?  I have a source saying that it would work if it were frictionless and we didn't try to extract energy from it (), so in a certain sense, it is very close to possible (they didn't provide a full analysis though.)  Another Image: has now probably made around 15 accounts. He consistently uses the , , ,  and  tags, and does not ever do anything constructive.  was his latest.  Unfortunately I haven't been bookmarking his other questions, but here are some of his previous accounts:          He has also gone by many other names (Iraq War Veteran is the one that comes to mind), but those accounts have been deleted.    Is there nothing we can do about this? Deleting and suspending his accounts just seems to give him more reason to create other accounts. Is there a way to block him entirely?    Edit:  seems to have been deleted by Community ♦ How to combine bold and "code sample" in Markdown? How can I make a word in a code sample bold? I only see asterisks around the expected bold text.  sample **sample** sample How can I see flags I cast from all sites? Prove that $f'(0)$ exists and $f'(0) = b/(a - 1)$ Problem:   If $f(x)$ is continous at $x=0$, and $\lim\limits_{x\to 0} \dfrac{f(ax)-f(x)}{x}=b$, $a, b$ are constants and $|a|&gt;1$, prove that $f'(0)$ exists and $f'(0)=\dfrac{b}{a-1}$.   This approach is definitely wrong:    \begin{align} b&amp;=\lim_{x\to 0} \frac{f(ax)-f(x)}{x}\\ &amp;=\lim_{x\to 0} \frac{f(ax)-f(0)-(f(x)-f(0))}{x}\\ &amp;=af'(0)-f'(0)\\ &amp;=(a-1)f'(0) \end{align}  I will show you a case why this approach is wrong:     \[f(x)= \begin{cases} 1,&amp;x\neq0\\ 0,&amp;x=0 \end{cases}\]   $\lim_{x\to0}\dfrac{f(3x)-f(x)}{x}=\lim_{x\to0} \dfrac{1-1}{x}=0$   but $\lim_{x\to0}\dfrac{f(3x)}{x}=\infty$,$\lim_{x\to0}\dfrac{f(x)}{x}=\infty$   Does anyone know how to prove it? Thanks in advance! Sex worker student offering her (lawful) services One of my students is an escort/stripper and she has offered me (and other faculty in my department) her "services". I am pretty sure my initial reaction of "thanks for letting me know, now can you answer the question about how to calculate the standard deviation", may not have been the best reaction. The offers have continued. My head of school is aware of the issue, and has asked if I want him to do anything.  Is the student doing anything wrong by offering her services to me? For what it is worth, prostitution is legal in the UK. Is this any different then a student telling me she works in a restaurant?  What is the correct response in a situation like this? For all square matrices $A$ and $B$ of the same size, it is true that $(A+B)^2 = A^2 + 2AB + B^2$? The below statement is a true/false exercise.  Statement: For all square matrices A and B of the same size, it is true that $(A + B)2 = A^2 + 2AB + B^2$.  My thought process: Since it is not a proof, I figure I can show by example and come to a valid conclusion based on such example.  My work:  Come up with a square matrix A and B let both be a 2 by 2 matrix(rows and cols must be same).  Matrix $A$:  $A = \begin{array}{ccc} 3 &amp; 5 \\ 4 &amp; 6 \\ \end{array} $  Matrix $B$:  $B =  \begin{array}{ccc} 5 &amp; 8 \\ 9 &amp; 4 \\ \end{array} $  $A + B =  \begin{array}{ccc} 8 &amp; 13 \\ 13 &amp; 10 \\ \end{array}$  $(A + B)^2 =  \begin{array}{ccc} 233 &amp; 234 \\ 234 &amp; 264 \\ \end{array}$  $A^2 =  \begin{array}{ccc} 29 &amp; 45 \\ 36 &amp; 56 \\ \end{array}$  $(AB) =  \begin{array}{ccc} 60 &amp; 44 \\ 74 &amp; 56 \\ \end{array}$  $2(AB) =  \begin{array}{ccc} 120 &amp; 88 \\ 234 &amp; 112 \\ \end{array}$  $B^2 =  \begin{array}{ccc} 97 &amp; 72 \\ 81 &amp; 88 \\ \end{array}$  $A^2 + 2AB + B^2 =  \begin{array}{ccc} 246 &amp; 205 \\ 265 &amp; 256 \\ \end{array}$  Based my above work, the answer is false.   Is there another way to approach the problem? It seems like a lot of work needed to be done for a true/false question which raised my suspicion about whether there is a better way to look at the problem. Equivalence of definitions of prime ideal in commutative ring Dynamic LINQ OrderBy on IEnumerable / IQueryable I found an example in the  for Dynamic LINQ that allows you to use a sql-like string (e.g. OrderBy("Name, Age DESC")) for ordering. Unfortunately, the method included only works on IQueryable&lt;T&gt;. Is there any way to get this functionality on IEnumerable&lt;T&gt;? Are there constants in JavaScript? Is there a way to use constants in JavaScript?  If not, what's the common practice for specifying variables that are used as constants? Layers with same coordinates not lining up I have a project where I have a few layers (State of Texas, cities, roads, etc.). They are all resaved and projected to NAD83 / UTM zone 14N EPSG: 26914. The project CRS is also NAD83 / UTM zone 14N EPSG: 26914 and on the fly projection is enabled. I added a text delimited file and cannot get them to line up. I checked the attribute table of the delimited file and the coordinates are correct. I cross-checked this with a point close to where a few of the points from the delimited file are and they are very close so in theory they should be lining up. I tried to save the delimited file and save it with the same projection and add the shp file back in and that did not work. Anyone have any ideas? I can't think of anything else to try. Integrated circuits seem to have standard voltages of 5 V, 3.3 V, 2.5 V, 1.8 V, etc.  Who decides these voltages? Why do smaller devices require lower voltages? If a function is a combination of other functions whose derivatives are known via composition, addition, etc., the derivative can be calculated using the chain rule and the like. But even the product of integrals can't be expressed in general in terms of the integral of the products, and forget about composition! Why is this? Is there a nice example of integral domain $R$ and $s,t \in R$, with $Rs \cap Rt$ not principal but lcm($s,t$) exists? I am currently searching for an integral domain $R$ which allows lcm, but where the intersection of two principal ideals is not necessarily a principal ideal (or at least an example with two certain elements).   As converse example (where the sum of two ideals is not principal but $R$ allows gcd) is $\mathbb Z[X]$. It allows gcd, but obviously $\left&lt;X+1,2\right&gt;$ is not principal.  An example of an integral domain where the intersection of two principal ideals is not principal would be $\mathbb Z[\sqrt{-5}]$ with the ideal $\left&lt;2\right&gt; \cap \left&lt;1+\sqrt{-5}\right&gt;$, but this doesn't allow lcm.  Since I can't find a nice example, I put the question here. Maybe someone has already seen this? (I am not completely sure, one even exists, but pretty certain there is an example. In the case my hunch is wrong, I would be happy, if someone could proof me wrong.) Launch shell scripts from anywhere Is it possible to run my scripts located in ~/scripts from anywhere?  Say i want to run ./scriptname regardless of my current working directory. How to prevent Windows from entering idle state? I installed Ubuntu 13.04 on my Vista 64 bit machine and I thought it was going to uninstall Vista but it didn't, now I have both systems.  How do I get rid of Vista? When did the 5-foot square/hex become the standard unit of measurement in Dungeons & Dragons?