Delta Definition and 1000 Threads

  1. S

    Is delta H a state function?(Hess Law?)

    is delta H a state function??(Hess Law?) Is delta H a state function? We know that delta H=delta U+W (at const P) so, we also know that W is path dependent function.So delta H being a sum of delta U and a path dependent function must not be a state function.(point 1) But there is this Hess...
  2. S

    Is delta H=0 for isothermal process?

    1.>Consider a gas in a vessel with a piston on top.Let it expand to a greater volume. So, delta H=delta U+delta(PV) but delta U is 0 as it is isothermal. now,as the number of moles of gas remains constant,delta(PV) is nR(delta T) which is again 0. SO delta H is 0. Thats what my book says...
  3. D

    Double Delta Function Potential Well

    Hello Again! My question: Find the bound energy spectrum of the potential that contains two delta-function wells: V(x) = -V_{0}\delta(x-\frac{a}{2}) -V_{0}\delta(x+\frac{a}{2}) under the assumption that the wells are located very far away from each other. Find and plot the associated stationary...
  4. J

    Delta function at integral limit

    I have a question about delta functions. What I want to believe is the following \int_{-\infty}^{0} \, dt \, f(t) \delta(t) = \frac{1}{2} f(0). It even shows up on Wikipedia (so it must be true!) Here is an argument (I know it isn't a proof). If I use the "delta-sequence" approach and...
  5. B

    Discourse on Dirac Delta Function in Spherical/Polar Coordinates

    Anyone know where I can find a discourse on the dirac delta function in spherical or polar coordinates, in particular why it is the form it is with correction coefficients? Thank you.
  6. L

    Using MATLAB to get the fourier transform of dirac delta function

    Homework Statement Dear all, I have a problem when I using MATLAB to get the Fourier transform of dirac delta function. below is my code.Homework Equations clear all; clc; close all; % t=0:0.002:2; t=0:0.002:4; dt=t(2)-t(1); u=zeros(size(t)); pos0=find(t>=1,1); u(pos0)=1/dt...
  7. U

    Gradient delta f of f= z^-1 * (sqrt((9x^2*y^2))

    Homework Statement Find delta f of f=Z^-1 * Sqrt(9x^2*y^2) at point (1,4,10) Homework Equations f =f+(fx*delta x )+(fydelta y)+(fz*delta z) The Attempt at a Solution fx = 9*2x/(z*(2*sqrt(9x^2*y^2)) =.18 plugging in (1,4,10) fy=2y/(z*(2*sqrt(9x^2*y^2)) =.08 fz=(sqrt(9x^2*y^2) )...
  8. J

    What is the result of taking the integral of δ(τ+2) - δ(τ-2)?

    hi guys i want to find i took the integral of δ(τ+2) and I said that it's basically u(t+2) δ(τ-2) is u(t-2) so we have u(t+2) - u(t-2) = 2 from -2 to 2.. well after that i need to get the absolute value of this and then the power of two, i don't know how to do this.. my book...
  9. T

    Constant Delta E-thermal in a given distance?

    In a given distance apparently regardless of how much work is done (whether the force is large or small) the change in thermal energy is the same since thermal energy change is fk times d. Since Fk is constant as is D the change in thermal energy of the system will remain constant. I'm having...
  10. M

    Why Does My Solution Differ From the Textbook in This Epsilon-Delta Problem?

    Homework Statement find an open interval about x0 on which the inequality lf(x)-Ll<\epsilon holds. Then give a value for \delta>0 such that for all x satisfying 0<lx-xol<\delta the inequality lf(x)-Ll<\epsilon holds f(x)=x2 L=3 x0=-2 \epsilon=0.5 Homework Equations The Attempt...
  11. Q

    What is the purpose of the Dirac delta function in three dimensions?

    i don't really understand the dirac delta function in 3D. is it right that integral of f(r)d3(r-a)dt = f(a) where a = constant ,r is like variable x in 1D dirac delta function? so why when i have f(r')d3(r-r') , it picks out f(r)? where r is now a constant and r' is a...
  12. F

    How Can I Prove Continuity Using Epsilon Delta Definition?

    Recently in adv calc we have been dealing with the epsilon delta definition for continuity, and my professor said that it is ok to assume that delta<1. I actually used this to show that x^4 satisfies the epsilon delta condition but I'm not quite sure why we can take delta<1. I am sure you guys...
  13. M

    Distribution Theory Delta Function

    [PLAIN]http://img820.imageshack.us/img820/5817/img8968h.jpg Any hints please, just starting question. Haven't really done any questions like this before
  14. C

    Dirac delta function under integral?

    Hello all, I joined this amazing forum just today.I hope that my question will get answered soon. So here it is.I am unable to understand a some steps in calculation. Please help me understand. Here is a linear homogeneous first order differential equation whose solution a research...
  15. J

    Vector field identity derivation using Einstein summation and kronecker delta.

    Homework Statement Let \vec{A}(\vec{r})and \vec{B}(\vec{r}) be vector fields. Show that Homework Equations \vec{\nabla}\bullet(\vec{A}\vec{B})=(\vec{A}\bullet\vec{\nabla})\vec{B}+\vec{B}(\vec{\nabla}\bullet\vec{A}) This is EXACTLY how it is written in Ch 3 Problem 2 of Schwinger...
  16. N

    Dirac delta, generalizations of vector calculus and sigh vagueness

    Although I am an aspiring physicist, I cannot cope with the physicist's love for vagueness when it comes to yielding math. Exactness is simply not a luxury that can be ignored, certainly not in theoretical physics. But okay, I realize the dirac delta function can be made exact by the use of...
  17. S

    Delta wye connection using 3 small transformers

    I am confused from a couple of diagrams I have about how to correctly wire 3 small transformers to form a delta wye connection. The transformers are labeled as Primary H1 H2, H1 H2, H1 H2 Secondary X2 X1, X2 X1, X2 X1 My question is in all the diagrams I have the Delta connections...
  18. A

    Understanding the Dirac Delta Distribution

    So I've been told that the Dirac delta functional is a distribution, but I don't see why that's the case. I had an introduction to distributions in my calculus IV course, but as I remember it, a distribution involves and integral containing a the product of a function from the Schwartz space and...
  19. M

    Laplace transform - Dirac delta

    i need help trying to find the laplace transform of te-t\delta(t) i know the laplace transform of te-t is 1/(s+1)2 but i don't know how to find the laplace transform of a product with the Dirac delta
  20. S

    Is the Dirac Delta Function Even?

    Hi this is my first post here so I'm sorry if my question seems trivial. I haven't worked a lot with the dirac delta function before, so i always thought that the shifting property would only work as: \int\delta(x-h)\;f(x)\;dx=f(h) Now I've been reading some articles and I came across...
  21. F

    Information content of Dirac delta function

    I understand that the Dirac delta function can be taken as a distribution. And that one can calculate the Shannon entropy or information content of any distribution. So what is the information content of the Dirac delta function? I think it is probably identically zero, but I'd like to see the...
  22. L

    Ship wing. Do they have to be Delta?

    I'm designing a new spacecraft model, but it does not use Delta wings, like most ships do. I need them to be efficient, because my ship is kinda large. (It's like a hybrid of a rocket, and the Space Shuttle), and so I have two questions: 1) My craft's wings look like really tall right...
  23. T

    Does Time-Energy Uncertainty Violate Energy Conservation?

    Hi folks, I am new to physics forums , an engineer by profession, I have newly developed some interest for pure physics, can someone please enlighten me on the violation of energy conservation by the time energy UP? The way I understand it the principle only puts a LOWER bound. Is...
  24. L

    How Do I Construct an Epsilon-Delta Proof for a Function Mapping R2 to R1?

    I have a problem on a take-home test, so I can't ask about the specific problem. So this is just going to be a general, how do I put stuff together problem. I have a function of x and y that maps R2 into R1. The limit as (x,y)->(0,0) is zero, and I've worked through the various paths already...
  25. T

    Is this delta epsilon proof correct?

    Homework Statement Show that Re(z) -> Re(z0) as z -> z0 The Attempt at a Solution let epsilon > 0, choose delta = epsilon, so |Re(z) - Re(z0)| = |(z + z')/2 - (z0 + z0')/2| (where z' and z0' are the complex conjugates) |(z + z')/2 - (z0 + z0')/2| = |(z - z0 + z' - z0')/2| < |z -...
  26. T

    Delta Epsilon Proof: Prove f(z)/g(z) \rightarrow w1/w2 as z\rightarrow z0

    Homework Statement Define: f(z) \rightarrow w1 as z \rightarrow z0 and g(z) \rightarrow w2 as z \rightarrow z0 prove that f(z)/g(z) \rightarrow w1/w2 as z\rightarrow z0 The Attempt at a Solution let \epsilon > 0 choose \delta > 0 such that: |f(z) - w1| < ______...
  27. M

    Understanding Epsilon Delta Limits Relationship in Calculus

    Homework Statement Is my understanding correct? As delta(y) and delta(x) approach X from points to the left and points to the right of X (x is what we wish to find the derivative of) then the x and y values of points to the left and right approach the x and y values of X. And as the...
  28. Q

    The Levi-Civita Symbol and Its Relation to the Kronecker Delta: A Closer Look

    hi, i don't understand why levi civita symbols is equal to kronecker delta when i was reading the wikipedia on it http://en.wikipedia.org/wiki/Levi-Civita_symbol namely, 1)why does EijkElmn = det [ 9 terms of kronecker delta] how do we know its those 9 terms? like dil dim din etc 2)and since...
  29. D

    Charge Density and Diract Delta Functions

    Homework Statement a) A charge q1 = q is at r'1 = -Di, and a charge q2 = -3q is at r'2 = Di. Find an expression for the volume charge density p(r). b) An infinitely long wire along the z-axis has a uniform linear charge density \lambda. Find an expression for the volume charge density p(r) in...
  30. A

    Using Epsilon Delta to prove a limit

    Homework Statement prove that the lim as x goes to 4 of x^2 + x -11 = 9 This is the example used on Paul's Online Notes on limits in calculus which can be found here http://tutorial.math.lamar.edu/Classes/CalcI/DefnOfLimit.aspx (I really like this resource.) Homework Equations Paul...
  31. R

    Can you bring out the delta x constant?

    Is this legal? I assumed that delta x is a constant that is approaching zero. So I brought it out. When I took the derivative, the delta x canceled out with the denominator. So I'm left with the derivative of the intergral of f(x) with respect to itself. So I'm essentially trying to find the...
  32. O

    Approximations to the delta function on a computer

    Hi, I am looking for approximations to the delta functoin which I can use on a computer. Although I will never get an exact delta function, I can make an approximation that it can be improved as much as I like. Would you help me to find the approximation of the delta function so that I can...
  33. S

    Two proofs in Dirac Delta Function

    Homework Statement a.) Given \delta_n=\frac{ne^{-{n^2}{x^2}}}{\pi} Show: x{\frac{d}{dt}\delta_n}=-\delta_n b.) For the finite interval (\pi,-\pi) expand the dirac delta function \delta(x-t) in sines and cosines, sinnx, cosnx, n=1,2,3... They are not orthogonal, they are normalized to...
  34. P

    Representation of Delta Function

    Hopefully people are still prowling the forums this close to christmas :) I want to show that sin(ax)/x is a representation of a delta function in the limit a->infinty i.e 1) It equals 0 unless x=0 2) integrated from plus minus infinity it equals 1 and 3) multiplying by an arbitrary...
  35. V

    Solving Delta G from a Solubility constant

    The Solubility Constant for AgI(s) at 25 degrees Celsius is 8.3*10^-17 how do i find \DeltaG(rxn) for [Ag+]=9.1*10^-9 & [I-]=9.1*10^-9 Using the equation: ΔG=ΔGº+RTln(Q) Let K=Our solubility constant: 0=ΔGº+RTlnK ΔGº=-RTlnK Now, ΔG=-RTlnK+RTlnQ ΔG=RTlnQ-RTlnK ΔG=RT(ln(Q/K)) ΔG=-5.67KJ/mol...
  36. M

    Uncertainty in measurements and epsilon delta definition of a limit

    does the epsilon delta definition of the limit connect to the uncertainty in measurements like this? like if we measure a quantity time with value a with error of + or - delta then my formula will give me v with value L +or - epsilon or is it unrelated?
  37. B

    Question on delta potential function

    NOT A HOME WORK QUESTION how do i know if a delta potential function is given if its solution is even or odd? do i look for symettry or something take this function for example: V(x)= -alpha[delta(x+a) + delta(xa)] i skeched the following graph. since V(-a)=V(a)...
  38. A

    Chemistry, Calorimetry finding delta H

    Homework Statement Sodium metal reacts with water to produce hydrogen gas and sodium hydroxide according to the equation: 2 Na(s) + 2 H2O(l) ? 2 NaOH(aq) + H2(g) When 0.030 mol of Na is added to water, the temperature of the calorimeter rises from 25.00C to 37.90C. If the heat...
  39. H

    Line charge density expressed via Dirac delta function

    Homework Statement Let's say we have a wire of finite length L with total charge Q evenly spread along the wire so that lambda=Q/L, linear charge density, is constant. The wire is shaped in x-y plane in some well behaved curve y = f(x). Find the surface charge density sigma(x,y). Homework...
  40. S

    Proving Vector Identities Using the Permutation Tensor and Kroenecker Delta

    Homework Statement Prove using the Levi-Civita Tensor/Kroenecker Delta that: (AxB)x(CxD) = (A.BxD).C-(A.BxC).D Homework Equations εіјkεimn = δjmδkn – δjnδkm (where δij = +1 when i = j and 0 when i ≠ j) The Attempt at a Solution if E = (AxB) then Ei = εіјkAjBk, and if F =...
  41. H

    Help Understanding Dirac Delta Function in Lecture Notes

    I don't understand in the first paragraph of the attached lecture notes. Could anyone help?
  42. R

    Dirac Delta as Gaussian functions

    I am looking at a problem, part of which deals with expressing delta dirac as a limiting case of gaussian function. I am aware of the standard ways of doing it. In addition, I would also like to know if the following are correct - \delta(x-a) = \lim_{\sigma \rightarrow{0}} \int_{a -...
  43. N

    Epsilon delta surroundings question

    i need to prove that for every delta i call d=delta e=epsilon 1/|x+1|>e we can choosr any e we want so they took e=1/4 but because the innqualitty needs to work for every delta they took x=min{2,(1+d)/2} for d>2 it takes x= 1+d /2 for d<2 takes x=2 uppon what logic they found this...
  44. D

    Infinite square well with delta potential

    Homework Statement I have infinite square well which has a potential V(x)=\frac{\hbar^2}{m}\Omega\delta(x) in x=0, and is 0 in the interval x\in[-a,a]Homework Equations Schrodinger eq.The Attempt at a Solution I solved the time independant Schrodinger eq. by integration around x=0 by some...
  45. A

    Solving for time when delta x=0?

    So my physics book says "from x(final)=x(initial)+V(initial)t+1/2at^2 observe that when x(final)=x(initial), the time is given by t=-2V(initial)/a" Now if change in x is equal to 0, wouldn't your velocity v(initial)t from above along with your acceleration also be zero? How is the book getting...
  46. L

    Can the Levi-Civita Kronecker Delta relation be proven using a matrix approach?

    This isn't a HW question just something I am curious about. I was looking on wikipedia and found a way to prive the Levi-Citiva Kronecker Delta relation that I hadn't seen before. The site claims \epsilon_{ijk}\epsilon_{lmn} = \det \begin{bmatrix} \delta_{il} \delta_{im} \delta_{in}\\...
  47. V

    Calculate \Delta H_{rxn}\circ for 2Al_{2}O_{3} to 4Al+3O_{2}

    \Delta H_{f}\circ=-1670kJ/mol for Al_{2}O_{3} What is \Delta H_{rxn}\circ for 2Al_{2}O_{3}(s)\rightarrow4Al+3O_{2}(g) So clearly we simply multiply -1670*2=-3340kJ/mol. The answer is actually POSITIVE 3340kJ/mol! Can someone please explain to me how this reasoning works? Thank you!
  48. F

    Multivariable Dirac Delta Functions

    Hello all. So I am trying to integrate a function of this form: \int\intF(x,y)\delta[a(Cos[x]-1)+b(Cos[y]+1)]dxdy The limits of integration for x and y are both [0,2Pi). I know that this integral is only nonzero for x=0, y=Pi. So this should really only sample one point of F(x,y)...
  49. D

    How to Prove \(\lim_{y\rightarrow0}\frac{y}{x^2+y^2}=\pi\delta(x)\)?

    What is the way to show that \lim_{y\rightarrow0}\frac{y}{x^2+y^2}=\pi\delta(x) ?
  50. L

    Fourier Transform and Dirac Delta Function

    Homework Statement I am new to FT and dirac delta function. Given the following signal: x\left(t\right)=cos\left(2\pi5t\right)+cos\left(2\pi10t\right)+cos\left(2\pi20t\right)+cos\left(2\pi50t\right) I use the online calculator to find me the FT of the signal, which is...
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