Delta Definition and 1000 Threads

  1. Julian102

    How to calculate the equivalent resistance using wye delta ?

    Homework Statement https://z-1-scontent-sin1-1.xx.fbcdn.net/hphotos-xtf1/v/t34.0-12/12435980_942112312550457_1708451532_n.jpg?oh=b29a5e9b2ff96bbf0e11932d081eb25e&oe=568A9B79 [/B] We need to find the equivalent resistance along A to B ie AB Homework Equations R=(1/R1 + 1/R2+...+1/Rn)^-1 ...
  2. B

    Delta Function Integration: Justified or Fudging?

    Hello, I feel like I am fudging these integrals a bit and would like some concrete guidance about what's going on. 1. Homework Statement Evaluate ##I = \int_{-1}^{1} dx \delta'(x)e^3{x} ## Homework EquationsThe Attempt at a Solution [/B] I use integration by parts as follows, ##u =...
  3. ognik

    MHB Find Fourier series of Dirac delta function

    Hi - firstly should I be concerned that the dirac function is NOT periodic? Either way the problem says expand $\delta(x-t)$ as a Fourier series... I tried $\delta(x-t) = 1, x=t; \delta(x-t) =0, x \ne t , -\pi \le t \le \pi$ ... ('1' still delivers the value of a multiplied function at t)...
  4. Lagraaaange

    Radioactive decay: Solve for delta t

    Homework Statement Two isotopes N1, N2. You are given the value of the proportions N1(t1)/N2(t1) and N1(t2)/N2(t2). From this calculate Δt. Homework Equations dN/dt = -λN The Attempt at a Solution Solve dN1/N = -λdt and dN2/N = -λdt obtain: N1(t2) = N1(t1)exp(-λ1(t2-t1)) (1) and N2(t2) =...
  5. M

    Transmission and Reflection Amplitude for Delta Potential SE

    This is not a homework question per se, but it's a simple enough computation question from some notes I'm reading that I think it belongs in this section. I will do my best to keep to you guys' formatThis is not a homework question per se, but it's a simple enough computation question from some...
  6. J

    Z = xy, dz/dx = delta z/ delta x, no idea why

    Homework Statement Ok this isn't really homework just something I came across and am confused by. I came across a function that looks similar to z = xy and I found that delta_z / delta_x = dz/dx which is really weird to me. This was really strange to me so I checked to see if z = x²y would...
  7. C

    Time dependent three dimensional dirac delta function

    Ok so for equations of spherical wave in fluid the point source is modeled as a body force term which is given by time dependent 3 dimensional dirac delta function f=f(t)δ(x-y) x and y are vectors. so we reach an equation with ∫f(t)δ(x-y)dV(x) over the volume V. In the textbook it then says that...
  8. kostoglotov

    Backwards difference matrix divided by negative delta x?

    An exercise in my text requires me to (in MATLAB) generate a numeric solution to a given second order differential equation in three different ways using a forwards, centered and backwards difference matrix. I got reasonable answers for \vec{u} that agreed with each other (approximately) for the...
  9. B

    Dirac Delta Function - Fourier Series

    1. Homework Statement Find the Fourier series of ##f(x) = \delta (x) - \delta (x - \frac{1}{2})## , ## - \frac{1}{4} < x < \frac{3}{4}## periodic outside. Homework Equations [/B] ##\int dx \delta (x) f(x) = f(0)## ##\int dx \delta (x - x_0) f(x) = f(x_0)##The Attempt at a Solution...
  10. P

    Kronecker Delta in Legendre Series

    Hello everyone, I'm working through some homework for a second year mathematical physics course. For the most part I am understanding everything however there is one step I do not understand regarding the steps taken to solve for the coefficients of the Legendre series. Starting with setting...
  11. Avatrin

    Epsilon delta definition of limit

    I am struggling to properly understand the \varepsilon-\delta definition of limits. So, f(x) gets closer to L as x approaches a. That is okay. However, taking the leap from there to the \varepsilon-\delta definition is something I have never really been able to do. Why is the formulation we...
  12. jk22

    Exploring the Dirac Delta Function

    I consider the Dirac delta. In physics the delta squared has an infinite norm : $$\int\delta (x)^2=\infty $$ But if i look at delta being a functional i could write : $$\delta [f]=f (0) $$ hence $$\delta^2 [f]=\delta [\delta [f]]=\delta [\underbrace {f (0)}_{constant function}]=f (0)$$ Thus...
  13. grandpa2390

    Evaluating integral with delta function (Fourier Transform)

    Homework Statement Evaluate the Following integrals 1. http://www4b.wolframalpha.com/Calculate/MSP/MSP10141fif9b428c5bab0b00005dc489hi851d28h7?MSPStoreType=image/gif&s=37&w=164.&h=35. Homework Equations...
  14. maverick_76

    How do I set up a delta potential well with an infinite potential wall?

    Okay so I am trying to solve a delta potential well with an infinite potential wall on one side a distance a away from the well. The other side is open so I am confused about how to set up the problem. Here is a picture of my work so far and if anyone has an insight into this I'd appreciate some...
  15. T

    Is the Delta current <30 degrees or not?

    The internet is really nebulous sometimes, I was looking and couldn't find the answer. I know that the line voltage is √3*Vphase<30degrees for a WYE. and that line current = √3*Iphase for a delta connection. But is that line current 30 degrees out of phase to the phase current? As the voltage...
  16. RaulTheUCSCSlug

    Delta T in Calorimetry always positive?

    For part number 5, it says to make sure that each ΔT is positive. Why is this? Couldn't it be a negative? Or does it have to be positive since if it wasn't you would be getting heat going in the wrong direction? Like the one substance would be gaining instead of losing the heat? Which would...
  17. V

    Delta Dirac 3d Dimensional Analysis

    1. I ´m trying to do the dimensional analysis of the Delta Dirac in 3 Dimensions. [PLAIN]http://[url=http://postimg.org/image/oif09fcd5/] 3. This is my atempt [PLAIN]http://[url=http://postimg.org/image/4qavbtv4p/]
  18. M

    Understanding the Use of the Delta Function in Probability Density Functions

    Homework Statement So I have an issue evaluating the integral for a joint probability distribution given by: Pr(R) = \displaystyle \int_{0}^{r_{max}}\int_0^{2\pi}\int_0^{\pi}\sin\theta \delta(R-r\sin\theta)d\theta d\phi dr where I know the relationship between r and R is given by...
  19. ddd123

    Microcanonical partition function - Dirac delta of operators

    Homework Statement Why is it that the microcanonical partition function is ##W = Tr\{\delta(E - \hat{H})\}##? As in, for example, Mattis page 62? Moreover, what's the meaning of taking the Dirac delta of an operator like ##\hat{H}##? Homework Equations The density of states at fixed energy is...
  20. T

    MHB Trouble with Delta Epsilon Problem

    I understand and can do part (a) of the problem but when it gets to part (b) I'm lost, how do I find/explain why there is no value of delta > 0 that satisfies the the problem.
  21. H

    A simple delta function properties, sifting property

    I don't know why this is possible To use delta function properties( sifting property) integral range have to (-inf ,inf) or at least variable s should be included in [t_0,t_0+T] but there is no conditions at all (i.e. t_0 < s < t_0+T) am I wrong?
  22. B

    Infinite potential well with delta well

    I Have tried to solve a problem about infinite potential well with a delta well in the middle, but I haven't the results and so I can't check if the proceeding is wrong... My attempt solution: The Schroedinger's Equation is: ##\psi''(x)=\frac{2m}{\hbar^2} (V(x)-E) \psi (x)## so we have...
  23. B

    Infinite well with delta well in the middle

    Homework Statement I Have tried to solve a problem about infinite potential well with a delta well in the middle, but I haven't the results and so I can't check if the proceeding is wrong. I post the steps that I have followed hoping someone can help me to understand. We have a particle in 1D...
  24. F

    Where is the mistake in this epsilon delta proof?

    The question asks to proof that the limit given in incorrect by contradiction. I tried working using the estimation method and the weird thing is that I completed the proof and found that the supposedly "incorrect" limit gave a correct answer although it was supposed to give me a contradiction...
  25. B

    How to handle squares of delta distributions

    Homework Statement I have to write equations of motion for a field, namely ## A ##. The full action has actually three terms, but my problem is with a part of the action reading: $$ S =\int d^{10}x \sqrt{-g} [ f(x_1, ... , x_{10}) + \delta (y) A ]^2 $$ In the 10 x's there is of course the...
  26. C

    Proving a Dirac delta property

    Homework Statement [/B] Prove that \delta[a(x-x_1)]=\frac{1}{a}\delta(x-x_1) Homework Equations In my attempt I have used \delta(ax)=\frac{1}{a}\delta(x) but I'm not sure I'm allowed to use it in this proof. The Attempt at a Solution Some properties of Dirac delta function are proven using...
  27. Terocamo

    Confusion Surrounding Dirac Delta Comb Sampling: Why is δ(0) Infinite?

    I have recently digged up a post in the forum about a confusion arise from definition of Dirac Delta function and I am actually really bothered by it (link to the thread). When people talk about sampling some function f(x) with Dirac Comb, or impulse train, they would be talking about the...
  28. avikarto

    Fortran [FORTRAN] FFT of delta function, issue w/ MKL & Intel compiler

    I am trying to program something using a backwards FFT, and am attempting to feed it a delta function as a test condition since this result is known. However, my results are nonsense compared to what is expected. It should be the case that if we have...
  29. K

    Scalar product and the Kronecker delta symbol

    From a textbook. proof that the scalar product ##A\centerdot B## is a scalar: Vectors A' and B' are formed by rotating vectors A and B: $$A'_i=\sum_j \lambda_{ij} A_j,\; B'_i=\sum_j \lambda_{ij} B_j$$ $$A' \centerdot B'=\sum_i A'_i B'_i =\sum_i \left( \sum_j \lambda_{ij} A_j \right)\left( \sum_k...
  30. ognik

    MHB Contour integral representation of Kronecker delta

    I'm rather impressed with complex analysis, but clearly I have a lot to learn. I'm told $ \frac{1}{2\pi i} \oint {z}^{m-n-1} dz $ is a rep. of the kronecker delta function, so I tried to work through that. I used $z = re^{i\theta}$ and got to $ \frac{1}{2\pi}...
  31. Deudoronomy

    It is a simple Delta G naught reaction problem

    Homework Statement Calculate Delta G naught rxn and K for the reaction: 2 Fe 3+ +2I- <--> 2 Fe 2+ +I2Homework EquationsThe Attempt at a Solution I came up with -.24 V for E naught and plugged it into ( -2*96.5*-.24) and got Delta G as 46.32 KJ but I don't know if this is right and I'm not...
  32. H

    Kronecker function products - matrix format

    Hi all, Firstly, I am not sure whether this is the area of the forum to ask this. I have been learning and researching a completely different topic, and from this I have come across a completely new concept of the Kronecker function. I have done a google search on this to get the intro and...
  33. Z

    What are some applications for the Dirac delta function in classical mechanics?

    Hey community, are there some application for the Dirac delta function in classical mechanics? Im interessted in some application of the famous delta function. If there applications can someone explain it? Greetings :)
  34. L

    Can someone help me out in solving for delta t

    Homework Statement Delta d = 0, v1 = 5.2 m/s, a = 9.8m/s^2 (down) delta t = ? Homework Equations d = v1 x t + 1/2 x a x t^2 The Attempt at a Solution 0 = (5.2 m/s) x t + 1/2 x (9.8 m/s^2) x t^2 0 = t(5.2m/s - 4.9 m/s^2 x t^2) This is a sample question and states the answer is delta t = 0 or...
  35. C

    Using the precise definition of a limit (epsilon & delta)

    I'm trying to practise, precise definition of a limit (epsilon & delta) Just to check I'm along the right lines here's a previous question to the one I'm stuck on If epsilon > 0 then there is delta >0 ... All that introduction stuff, then Lim x-> 2 (3x-1) =5 Hence |x-2| < delta then |3x - 6|...
  36. B

    How to correctly convolve two delta functions?

    How do I correctly compute the convolution of two delta functions? For example, if I want to compute ##\delta(\omega)\otimes\delta(\omega)##, I should integrate $$\int_{-\infty}^\infty \delta(\omega-\Omega)\delta(\Omega) d\Omega$$ This integrand "fires" at two places: ##\Omega = 0## and...
  37. L

    Special relativity - four current and dirac's delta

    Homework Statement Hello, in my special relativity course we are making the (electrical charge) current a four-current. I have serious problems understanding the following: http://imageshack.com/a/img540/2046/8IYpxu.png In particular, on line 2, in the last equation, I don't understand why...
  38. Z

    Exploring Dirac Delta Function: Using to Express 3D Charge Distributions

    Hello community, this is my first post and i start with a question about the famous dirac delta function. I have some question of the use and application of the dirac delta function. My first question is: Using Dirac delta functions in the appropriate coordinates, express the following charge...
  39. C

    Simplifying Argument of Dirac Delta for Reexpressing a Dirac Delta

    Homework Statement Show that $$\delta(k^2) \delta[(k-q_2)^2] = \delta(k^2) \delta(k^0 - \sqrt{s}/2) \frac{1}{2\sqrt{s}},$$ where ##k = (k^0, \mathbf k)## and ##s = q_2^2,## where ##q_2 = (\sqrt{s},\mathbf 0)## 2. Homework Equations I was going to use the fact that $$\delta(f(x)) = \sum...
  40. K

    Epsilon delta limits if/then language

    < Mentor Note -- thread moved to HH from the technical math forums, so no HH Template is shown > This is from the question list at the UC Davis Website epsilon delta exercise list. In the exercise list we have: Prove that Which concludes with: Thus, if , it follows that...
  41. ShayanJ

    Rigorousness of this Dirac delta formula

    Is the following equation mathematically rigorous? How can you tell? ## \int_{-\infty}^\infty \delta(x-a) \delta(x-b) dx=\delta(a-b)## Thanks
  42. W

    Understanding the Epsilon Delta Definition of a Limit

    Hi I'm new to limits and calculus in general. Our professor told us there existed some rigorous proof for a limit, but it was "beyond the scope of the course". All we needed to know about a limit was that (1)$$\lim_{x\to a} f(x)$$ is true iff when x approaches a from both directions p(x)...
  43. Coffee_

    Poisson equation with a dirac delta source.

    Consider: ##\nabla^{2} V(\vec{r})= \delta(\vec{r})## By taking the Fourier transform, the differential equation dissapears. Then by transforming that expression back I find something like ##V(r) \sim \frac{1}{r}##. I seem to have lost the homogeneous solutions in this process. Where does this...
  44. ranju

    Open Delta System: Finding kVA Rating of V-V Bank

    While studying a numerical on open delta system .., we have to find total kVA rating of V-V bank so obviously it should be equal to = root 3 *(kVA rating per transformer in V-V bank).. But in the solution , its is taken as =root 3 *(kVA rating per transformer in delta-delta )..! So , isn't it a...
  45. Dethrone

    MHB Proof of $\lim_{{n}\to{\infty}}a_n=\lim_{{n}\to{\infty}}b_n$ with $\epsilon-N$

    Let ${a_n}$ and ${b_n}$ be two convergent sequences such that $\lim_{{n}\to{\infty}}|a_n-b_n|=0$. Give an $\epsilon-N$ proof to show that $\lim_{{n}\to{\infty}}a_n=\lim_{{n}\to{\infty}}b_n$. Right now, I've just said without loss of generality, assume that $a_n>b_n$ for all $n>N$, then since...
  46. Dethrone

    MHB How to Prove Limit 2^n/n! Using Epsilon Delta?

    Using epsilon delta, prove $$\lim_{{n}\to{\infty}}\frac{2^n}{n!}=0$$ Doesn't seem too difficult, but I have forgotten how to do it. Obvious starting point is $\forall \epsilon >0$, $\exists N$ such that whenever $n>N,\left|\frac{2^n}{n!} \right|<\epsilon$.
  47. J

    Caculation of line current on a 3 phases unbalanced delta

    Hello, I cannot find back from school, the formula to use: A 3 phases 220Vac system, no neutral, 3300W of pure resistance load between L2 and L3, the same load between L1 and L3, nothing between L1 and L2. What will be I1, I2, I3 the current in the 3 lines of the network? Thanks in advance -- Jmp0
  48. D

    Strength of Dirac Delta Potential

    When talking about the strength of a delta potential , the delta potential is multiplied by a parameter ie α but how does a delta potential have a strength ? It is zero everywhere and infinite at x = 0. The parameter makes no difference to zero or infinity.
  49. K

    Star Delta Line/Phase Voltage Confusion

    As I am new to this forum, I must apologise if I have began this thread in the wrong category but I have a bit of a problem. I don't necessary study physics, I study Electrical Installation at college. As a result we overlap on some physics topics We have recently covered Star Delta. Now, I...
  50. Teemo

    How Do You Solve a Delta T Analysis Problem in Homework?

    Homework Statement See Thumbnail. Homework Equations N/A The Attempt at a Solution I am absolutely floored as how to do this problem.
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