Delta function Definition and 366 Threads

I have a line charge of length L and charge density /lambda on the Z-axis. I need to express the charge density in terms of the Dirac Delta function of theta and phi. How would I go about doing this?

I am trying to evaluate the following integral. \int_{-\infty}^{\infty}{\delta(2t-3)\sin(\pi t) dt} where delta represents the Dirac delta function. I am told that the answer is -1. However, when I evaluate it in MATLAB and Maple 11, I get an answer of -1/2. What is the correct way...

Homework Statement Can u pls help me to prove delta function. Here is the problem in attachment. Homework Equations The Attempt at a Solution

Homework Statement I'm trying to prove that \delta'(y)=-\delta'(-y). Homework Equations The Attempt at a Solution I'm having trouble getting the LHS and the RHS to agree. I've used a test function f(y) and I am integrating by parts. For the LHS, I have...

Homework Statement Hi there, I'm stuck at a problem where I have (sorry i don't know how to use mathtype so I'll try my best at making this clear) the integral of a dirac delta function squared: int[delta(x*-x)^2] between minus infinity and infinity (x*=constant) I know that the function...

Homework Statement If we have a delta function in cartesian coords, how do we convert it into spherical. for example : delta (r) = delta(x-x0) delta(y-y0) delta(z-z0) Homework Equations The Attempt at a Solution I used delta (r) = delta(r-r0) delta(cos{theta}-cos{theta0}) delta...

1. The ProblemHomework Statement 4 Parts to the Assignment. Finding the Displacement of a beam assuming w to be constant. 1. Cantilever beam, free at one end. Length =l, Force P applied concentrated at a point distance rl from the clamped end. Boundary Conditions y(0)=0, y'(0)=0, y"(l)=0, and...

I have two related questions. First of all, we have the identity: \int_{-\infty}^{\infty} e^{ikx} dk = 2 \pi \delta(x) I'm wondering if it's possible to get this by contour integration. It's not hard to show that the function is zero for x non-zero, but the behavior at x=0 is bugging...

[b]1. Homework Statement \int x[delta(x)-delta(x/3+4)] dx Homework Equations so I'm supposed to use this principle: \int f(x)delta(x-xo)dx=f(xo) The Attempt at a Solution So it seems simple but I just want to make sure that I'm applying the above principle correctly. I...

[SOLVED] Delta Function Well and Uncertainty Principle Homework Statement Griffiths Problem 2.25. I need to calculate < p^{2}> for the Delta Function Well. The answer given is: < p^{2}> = (m\alpha/\hbar)^2 The wave function given by the book is...

Homework Statement SO I'm given a dirac delta function, also known as a unit impulse function. d(t-t'_=(1/P) sum of e^[in(t-t')], for n from negative to positive infinity. I need to graph this. Homework Equations I understand that at t', there is a force made upon the system which...

So I'm studying that part right now. I only get parts of it though, it seems. The first thing the book goes over (This is intro to QM by Griffiths) is a potential that has the form -A*deltafunction. Okay, that's just something he plucked for simplicity. But then if the potential is lower...

Homework Statement Why does it make sense that a negative delta function potential represents a highly localized attractive force and a positive delta function potential represents a highly localized repulsive force? How do you explain that using -dV/dx = f(x) ? I guess I am confused about...

I'm trying to plot the function f(x,y) = DiracDelta[r-r0]and then take the Fourier transform. Is this a radial delta function? I'm having trouble understanding the significance of this "function" . Thanks!

for linear time invariant system, y(t)=h(t)*x(t) where y(t) is the output , x(t) is the input and h(t) is the impulse response.(* is the convolution) The definition of convolution is y(t)=integration from -infinity to +infinity (h(tau)x(t-tau)d(tau) p/s: i don't know how to use...

Homework Statement Evaluate: \int_{-3}^{5} e^{-2t} sin(t-3) \delta(t-5) dt Homework Equations \int_{-\infty}^{\infty} f(t) \delta(at-t_0) dt = \frac{1}{|a|}f(\frac{t_0}{a}) The Attempt at a Solution e^{-2(5)} sin (5-3) = e^{-10} sin (2) The solution given by the professor...

Evaluate: \int^{\infty}_{-\infty} f(x)\delta(x-x_0)dx Where f(x)=ln(x+3), x_0=-2 Ordinarily, you would just evaluate f(x_0), so it would be 0, but in this case, since f(x) is -\infty at x=-3, does that make a difference?

Homework Statement I'm having some trouble understanding the Kronecker Delta function and how it is used. I understand the basics of it, if i=j, delta=1, if not, delta=0. However, I don't understand why: \delta_{ii}=3 and \delta_{ij}\delta_{ij}=3Homework Equations \delta_{ij}=...

Homework Statement \int^{A}_{-A}\int^{Bx}_{-Bx}c\delta(xcos\varphi+ysin\varphi-d)dydx where A, B, c, d are constant Homework Equations The Attempt at a Solution I have tried a few different ways to integrate this, but am completely confused with what happens to this kind of delta...

OK, I'm currently reading Hughes' Finite Element Method book, and I'm stuck on a chapter the goal of which is to prove that the Galerkin solution to a boundary value problem is exact at the nodes. So, the author first speaks about the Dirac delta function: "Let \delta_{y}(x) = \delta(x-y)...

Dear all I'm wondering if you can help me find the most general formula of all nascent delta functions. all i have found a somewhat random forms . I'm looking for a general elegant formula that all the forms can be derived from . thanks in advance .

We know that div \; (\hat{r} / r ) = 4 \pi \delta (r) Why is there no generalized function (distribution) for div \; (\hat{r} / r^2) = ??

Dirac developed his delta function in the context of QM. But there are various functions under the integral that give the delta function. My question is does one Dirac delta function equal any other? Are all ways of getting the Dirac delta function equivalent? Thanks.

Homework Statement int[d(x-a)f(x)dx]=f(a) is the dirac delta fn but is int[d(a-x)f(x)]=f(a) as well? If so why?The Attempt at a Solution Is it because at x=a, d(0)=infinite and integrate dirac delta over a region including x=0 when d(0) is in the value in the integral will produce 1 hence f(a).

Hi I am not a mathematician so my question might be silly. I really came across it in physics but I think it is purely mathematical: I came across an equation of the form: delta(m-n)*A= delta(m-n)*B my question is now for what cases can I conclude A=B? Does this only hold for m=n, or can I...

Dear all, I need a simple proof of the following: Let [tex]u \in C(\mathbb{R}^3)[\tex] and [tex]\|u\|_{L^1(\mathbb{R}^3)} = 1[\tex]. For [tex]\lambda \geq 1[\tex], let us define the transformation [tex]u\mapsto u_{\lambda}[\tex], where [tex] u_{\lambda}(x)={\lambda}^3 u(\lambda...

I can remember from Differential Equations that any function convolved with a delta function results in a copy of the function located at the impulese. That is, x(t) * \delta(t-5) = x(t-5) However, I can't remember why. This is really irritating me since I need to use this concept for my...

Homework Statement How many stationary states exist for this potential? What are the allowed energies if the strength of the well, \alpha= \hbar^2/ma and \hbar^2/4ma where a= the position of the well(one at a, one at -a) Homework Equations V(x) = -\alpha(\delta(x+a) +\delta(x-a)) E_{one...

Homework Statement My question asks me to sketch the following: g(x) = \delta (y+a) + \delta (y) + \delta (y-a) Homework Equations The Attempt at a Solution I think this is it, but am I correct? I don't recall actually seeing a delta function other than a Kronicker(sp?) delta...

A vector function V(\vec{r}) = \frac{ \hat r}{r^2} If we calculate it's divergence directly: \nabla \cdot \vec{V} = \frac{1}{r^2} \frac{\partial}{\partial r} \left( r^2 \frac{1}{r^2} \right) = 0 However, by divergence theorem, the surface integral is 4\pi . This paradox can be solved by...

let f(y)=\int_0^2 \delta(y-x(2-x))dx. Find f(y) and plot it from -2 to 2. I know how to calculate \delta (g(x)) but i am not sure how to treat it with the y. I thought possibly to solve the quadratic in the delta function to find what x will equal for the roots in terms of y and got...

https://www.physicsforums.com/showthread.php?t=73447 I saw the above tutorial by arildno and looked at how he defined the Dirac Delta "function" as a functional. But isn't there a more easier way to do this. I have seen the following definition in a lot of textbooks. \delta(t) \triangleq...

I often see this in electrodynamics in the form of a point charge density function. There are some rules on how to manipulate the thing in integrals. But what is it mathematically?

I found this equation in a field theory book, which I can't figure how it was derived: \delta(x-a) \delta(x-a) = \delta(0) \delta(x-a)

Given a delta function barrier located at x=0: V(x) = +a * delta(x) If you have a particle incident from the left with E<0, what does the wave function look like?? I have trouble with this because I thought the particle energy needed to be greater than the minimum potential (E > Vmin) for...

I have a time dependent wavefunction for inside a delta function potential well: V(x) = -a delta(x). It reads Psi(x,t) = (sqrt(m*a)/hbar) * exp(-m*a*abs(x)/hbar^2) * exp(-iEt/hbar) I'm supposed to stick this back into the time dependent Schrodinger Equation and solve for E. Taking my...

[FONT="Arial"][FONT="Arial"]Hello, What is the dirac delta function and how is it different from a probability distribution?

Suppose that we take the delta function \delta(x) and a function f(x). We know that \int_{-\infty}^{\infty} f(x)\delta(x-a)\,dx = f(a). However, does the following have any meaning? \int_{-\infty}^{\infty} f(x)\delta(x-a)\delta(x-b)dx, for some constants -\infty<a,b<\infty.

Just have a question about the dirac delta function. I understand how you would write it if you want to shift it but how would you scale it assuming we are using discrete time. Would you write 2*diracdelta[n] or diracdelta[2n]. Also, would that increase it or reduce it by 2 meaning that...

I've recently come across this function in one of my science classes and am wondering were this identity comes from: \displaystyle{\int{\delta(t-\tau)f(\tau)d\tau}=f(t)} Where \delta(t) is the dirac delta function and f(t) is any (continuous?) function.

How can I prove that no continuous function exists that satisfies the property of the dirac delta function? I thought it should be pretty easy, but it's actually giving me quite a hard time! I know that the integral of such a function must be 1, and that it must also be even (symmetric about the...

I'm trying to show that \int \delta \prime(x-x')f(x') dx = f\prime(x) can I differentiate delta with respect to x' instead (giving me a minus sign), and then integrate by parts and note that the delta function is zero at the boundaries? this will give me an integral involving f' and delta...

I am reading a electrical engineering book about digital signal processing, in the process, those Fourier transform and discrete time Fourier transform of constant and the exponential function lead to the delta function. I understand how to manipulate them formally, but I have serious trouble...

Hello, I need to prove (7) here: http://mathworld.wolfram.com/DeltaFunction.html http://mathworld.wolfram.com/images/equations/DeltaFunction/equation5.gif The instructions were to start with the definition of the delta function by integral, and then chagne variables u -> g(x). But I...

As I read in my quantum mechanics book the delta function is sometimes called the sampling function because it samples the value of the function at one point. \int {\delta (x - x')} f(x')dx' = f(x) But then I opened a quantum field book and I found equations like that: \phi (x) =...

1st question what the heck does a "minimum" mean when talking about interference in waves, i got a question of the like y = 1.19(1 + 2 cos p)sin(kx - wt + p) is the superpostion function of three waves one which is p out of phase of the first and another which is p out of phase of the second...

Hello everyone, i have this question and not even sure how to approach it: \frac {di}{dt}+4i+3\int_{0^-}^t{i(z)dz = 12(t-1)u(t-1) and i(0^-) = 0 find i(t) last topics we covered were laplace transforms (and inverse) and dirac delta function. At least some hint to get me started...

hello again, i have an integral to solve and not sure how to approach this: \int f(q+T)\delta (t-q)dq and the boundaries of integral are -inf +inf couldn't figure it out with latex. what I know about this is that if delta function is integrated like this, it would be just the value of...

For a given function: r^n\hat r, find its curl. I formulated the divergence first. For the divergence: \nabla . (r^n\hat r) = (n+2)r^{n-1} and the functon becomes a dirac delta at the origin in case of n = -2. For the curl: Geometrically, the curl should be zero. Likewise, the curl in...

Can someone help me understand the transition between these two steps? <x> = \iint \Phi^* (p',t) \delta (p - p') \left( - \frac{\hbar}{i} \frac{\partial}{\partial p} \Phi (p,t) \right) dp' dp = <x> = \int \Phi^* (p,t) \left( - \frac{\hbar}{i} \frac{\partial}{\partial p} \Phi (p,t)...