What is Laplace equation: Definition and 161 Discussions
In mathematics and physics, Laplace's equation is a second-order partial differential equation named after Pierre-Simon Laplace who first studied its properties. This is often written as
∇
2
f
=
0
or
Δ
f
=
0
,
{\displaystyle \nabla ^{2}\!f=0\qquad {\mbox{or}}\qquad \Delta f=0,}
where
Δ
=
∇
⋅
∇
=
∇
2
{\displaystyle \Delta =\nabla \cdot \nabla =\nabla ^{2}}
is the Laplace operator,
∇
⋅
{\displaystyle \nabla \cdot }
is the divergence operator (also symbolized "div"),
∇
{\displaystyle \nabla }
is the gradient operator (also symbolized "grad"), and
f
(
x
,
y
,
z
)
{\displaystyle f(x,y,z)}
is a twice-differentiable real-valued function. The Laplace operator therefore maps a scalar function to another scalar function.
If the right-hand side is specified as a given function,
h
(
x
,
y
,
z
)
{\displaystyle h(x,y,z)}
, we have
Δ
f
=
h
.
{\displaystyle \Delta f=h.}
This is called Poisson's equation, a generalization of Laplace's equation. Laplace's equation and Poisson's equation are the simplest examples of elliptic partial differential equations. Laplace's equation is also a special case of the Helmholtz equation.
The general theory of solutions to Laplace's equation is known as potential theory. The solutions of Laplace's equation are the harmonic functions, which are important in multiple branches of physics, notably electrostatics, gravitation, and fluid dynamics. In the study of heat conduction, the Laplace equation is the steady-state heat equation. In general, Laplace's equation describes situations of equilibrium, or those that do not depend explicitly on time.
for the boundary conditions for this problem I understand that Electric field and Electric potential will be continuous on the boundaries.
I also know that I can set the reference point for Electric potential, wherever it is convenient. This gives me the fifth boundary condition. I am confused...
Hi Pfs,
I read these slides:
https://indico.math.cnrs.fr/event/782/attachments/1851/1997/Connes.pdf
It is about non commutative geometry (Alain Connes)
After Shapes II, you see a the plots of the square roots of a sequence of numbers given below:
5/4, 2, 5/2, 13/4 ....
I think that they are the...
I am trying to model the voltage function for a very long cylinder with an assigned surface charge density or voltage.
Then the solution inside the cylinder is:
$$\sum_{n=0}^{\infty}A_n r^n cos(nθ)$$
And$$\sum_{n=0}^{\infty}A_n r^-n cos(nθ)$$
outside. Is that correct
Knowing that we are in equilibrium ##\frac{\partial}{\partial t} = 0##.
We now have a Laplace's equation ##\kappa \frac{\partial^2 T}{\partial x^2} = 0##
I separated the rod in 2 halves.
The solution of this equation is ##\kappa_1 \frac{\partial2 T}{\partial x2} = C_1##
Integrating both side...
I tried to find a solution to the Laplace equation using spherical coordinates and the separable variable method. However, I found equations that I simply don't know how to find a solution. Thus, I tried in cylindrical coordinates with an invariance in ##\theta## but now I'm facing this...
Hello All,
I'm trying to create equation which can describe relation between electric fields of three coupled-lines and coupling between them. Let we say that, we have thee lines having infinit length which are placed above ground plane in distance h. The distance between coupled lines is...
Why doesn't the **Laplace's equation**(#\nabla^2V=0#) hold in the region within the sphere when there is a charge inside it ? Is it because #ρ \ne 0# within the sphere and it becomes a **poisson equation**($\nabla^2V=\dfrac{-ρ}{ε_0}$) and changes the characteristics of **Harmonic Solution**...
Is there a way to solve Laplace’s Equation on irregular domains if the domain’s shape is given by a function for example a 2D parabolic plate. I keep seeing numerical methods but I want to know is there an ANALYTICAL method to solve it on an irregular domain. If there isn't are there approximate...
There is a nice uniqueness theorem of electrostatics, which I have found only after googling hours, and deep inside some academic site, in the lecture notes of Dr Vadim Kaplunovsky:
Notice that the important thing here is that only the NET charges on the conductors are specified, not their...
I've been able to prove the following inequality $$\frac{2\pi\epsilon_0}{\log\left(\frac{b_1b_2}{a_1^2}\right)}\leq C \leq \frac{2\pi\epsilon_0}{\log\left(\frac{a_1a_2}{b_1^2}\right)}$$ but have no clue how to obtain exact value. Can someone check whether this inequality is correct and show how...
I have tried to Fourier transform in ##x## and get the result in the transformed coordinates, please check my result:
$$
\tilde{u}(k, y) = \frac{1-e^{-ik}}{ik}e^{-ky}
$$
However, I'm having some problems with the inverse transform:
$$
\frac{1}{2\pi}\int_{-\infty}^\infty...
How to run a numerical simulation of Laplace equation if one of the boundary condition is like this: $$V(x,y) = 0 \text{ when } x \to \infty$$
I am trying to use Python to plot the solution of this Example 3.5. in Griffins EM
Hello,
I have to prove that the complex valued function $$f(z) = Re\big(\frac{\cos z}{\exp{z}}\big) $$ is harmonic on the whole complex plane.
This exercice immediately follows a chapter on the extension of the usual functions (trigonometric and the exponential) to the complex plane, so I tend...
From Gauss's Law
give ##E=\dfrac{\sigma}{2\epsilon_0}##
##\therefore P_e=\dfrac{\sigma^2}{2\epsilon_0}##
Consider at equilibrium (before bubble being charged)
##P_i=P_0+\dfrac{4S}{R}##
Using Newton's 2nd Law
##\Sigma F=m\ddot{R}##
Let ##R+\delta R## be the new radius
Give (after binomial...
I was initially curious by the fact that streamlines around a circle appear the same as the lines of stress around a hole:
I understand that streamlines are the contour lines of the stream function ##\psi## which satisfies the Laplace equation. I was wondering there is a related function for...
Assume that an infinite metallic plate A lies in the xy-plane, and another infinite metallic plate B is parallel to A and at height z = h.
The potential of plate A is 0, and the potential of plate B is constant and equal to V.
So, there is a uniform electrostatic field E between plates A and B...
After looking around a bit, I found that, considering the polar axis to be along the direction of the point charge as suggested by the exercise, the following Legendre polynomial expansion is true:
$$\begin{equation}\frac{1}{|\mathbf{r} - \mathbf{r'}|} = \sum_{n=0}^\infty...
Imagine to be in 2 dimensions and you have to find the potential generated by 4 point-charges of equal charge located at the four corners of a square.
To do that I think we simply add all the contributions of each single charge:
$$V_i(x, y) = - \frac k {| \mathbf r - \mathbf r_i|}$$
$$ V(x, y)...
Homework Statement
I have a value of $$ U=U_0+x (∂U/∂x)+y(∂U/∂y)+z (∂U/∂z)+1/2x^2(∂^2U/∂x^2)+1/2y^(2∂^2U/∂y^2)+...$$
We need to find the mean value of the U. So the answer is
$$\overline{\rm U}\approx U_0+a^2/24(∇^2U)$$Homework Equations
$$\overline{\rm U}=1/a^3 \int \int\int Udxdydz$$
The...
Homework Statement
There's a metal cunducting cube with edge length ##a##. Three of its walls: ##x=y=z=0## are grounded and the other three walls: ##x=y=z=a## are held at a constant potential ##\phi_{0}## . Find potential inside the cube.
Homework Equations
The potential must satisfy Laplace...
Hi PF!
I looked through the documentation on their website, but under the tab "Solve partial differential equations over arbitrarily shaped regions" I am redirected to a page that does not specify how to create a region. Any help is greatly appreciated.
Also, if it helps, the domain is a...
can anyone help me on how I can map an isosceles trapezoid onto a rectangular/square domain.Actually I need to solve Laplace equation(delta u = 0) over this isosceles trapezoidal domain. Schwarz Christoffel mapping may help me. But can anyone give me any hint on this mapping procedure?
Hello! (Wave)
I want to solve the Laplace equation on the unit disk, with boundary data $u(\theta)=\cos{\theta}$ on the unit circle $\{ r=1, 0 \leq \theta<2 \pi\}$. I also want to prove that little oscillations of the above boundary data give little oscillations of the corresponding solution of...
Hi,
I am looking for the solution to the quadrant problem of the Laplace equation in 2 dimensions with Dirichlet boundary conditions
\begin{equation}
\frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} = 0
\end{equation}
in the first quadrant ## x, y \geq 0 ## with boundary...
Hello! (Wave)
Let $a,b>0$ and $D$ the rectangle $(0,a) \times (0,b)$. We consider the boundary value problem in $D$ for the Laplace equation, with Dirichlet boundary conditions,
$\left\{\begin{matrix}
u_{xx}+u_{yy}=0 & \text{ in } D,\\
u=h & \text{ in } \partial{D},
\end{matrix}\right.$...
Homework Statement
Solve the Laplace equation in 2D by the method of separation of variables. The problem is to determine the potential in a long, square, hollow tube, where four walls have different potential. The boundary conditions are as follows:
V(x=0, y) = 0
V(x=L, y) = 0
V(x, y=0) = 0...
The time-dependent Schrodinger equation is given by:
##-\frac{\hslash^{2}}{2m}\triangledown^{2}\psi+V\psi=i\hslash\frac{\partial }{\partial t}\psi##
Obviously, there is a laplacian in the kinetic energy operator. So, I was wondering if the equation was rearranged as...
I am solving the Laplace equation in 3D:
\nabla^{2}V=0
I am considering azumuthal symmetry, so using the usual co-ordinates V=V(r,\theta). Now suppose I have two boundary conditions for [V, which are:
V(R(t)+\varepsilon f(t,\theta),\theta)=1,\quad V\rightarrow 0\quad\textrm{as}\quad...
Homework Statement
An Ohmic material with some conductivity has a uniform current density J initially. Let's say the current is flowing in the direction of the z-axis. A small insulating sphere with radius R is brought inside the material. Find the potential outside the sphere.
Homework...
Homework Statement
The problem states:
"A point charge q is located at a fixed point P on the internal angle bisector of a 120 degree dihedral angle between two grounded conducting planes. Find the electric potential along the bisector."
Homework Equations
ΔV = 0
with Dirichlet boundary...
Dear all,
I would need mathematical help to solve for the temperature field in an annular geometry (you find a picture attached below the text):
A copper pipe containing a boiling two-phase flow (in the stratified regime) is immersed in a liquid bath, which temperature ##T_{IY}## is assumed to...
Homework Statement
Two concentric cylinders with radii a & b (b>a) with an infinitely long grounded strip along the z-direction are given potentials \phi_1 and \phi_2.
Find \Phi(r,\phi) for a<r<b
Boundary conditions:
\Phi(r,2n\pi)=0
\Phi(a,\phi)=\phi_1
\Phi(b,\phi)=\phi_2
Homework...
Hi PF!
I am considering a partial cylinder filled with fluid. By partial I mean consider something like a half-pipe. If a small disturbance is present, the fluid radius on the open side of the cylinder is ##r=R(1+\epsilon f(\theta,z,t))##. The Young-Laplace equation for capillary pressure is...
Homework Statement
House: a room (see figure) has perfectly isolated walls, except the two windows
where a convective heat exchange takes place (with the same transfer coefficient).
Outside temperature in front of a sun-faced wall-sized panoramic window is T1,
while at the back it is...
I am studying the linear oscillation of the spherical droplet of water with azimuthal symmetry. I have written the surface of the droplet as F=r-R-f(t,\theta)\equiv 0.
I have boiled the problem down to a Laplace equation for the perturbed pressure, p_{1}(t,r,\theta). I have also reasoned that...
Q) A conducting sphere of radius R floats half submerged in a liquid dielectric medium of permittivity e1. The region above the liquid is a gas of permittivity e2. The total free charge on the sphere is Q. Find a radial inverse-square electric field satisfying all boundary conditions and...
Hi,
I need to solve Laplace equation ##\nabla ^2 \Phi(z,r)=0## in cylindrical coordinates in the domain ##r_1<r<r_2##, ##0<z<L##.
The boundary conditions are:
##
\left\{
\begin{aligned}
&\Phi(0,r)=V_B \\
&\Phi(L,r)=V_P \\
& -{C^{'}}_{ox} \Phi(x,r_2)=C_0 \frac{\partial \Phi(x,r)}{\partial...
Hi. I have this problem in trying to solve this PDE analytically.
The PDE is represented by this diagram:
Basically this is solving the Laplace equation with those insulated boundaries except it has that point diffusing its value across the plane. I know how to solve the Laplace equation...
Consider an inﬁnitely long hollow dielectric cylinder of radius a with the electricpotential V = V0 cos φ on the surface of the cylinder where φ is an angle measured around the axis of the cylinder. Solve Laplace’s equation to ﬁnd the electric potential everywhere in space.Do you just plug V...
Homework Statement
Consider the Laplace Equation of a semi-infinite strip such that 0<x< π and y>0, with the following boundary conditions:
\begin{equation}
\frac{\partial u}{\partial x} (0, y) = \frac{\partial u}{\partial x} (0,\pi) = 0
\end{equation}
\begin{equation}
u(x,0) = cos(x)...
Suppose u(x,y) and v(x,y) are harmonic on G and c is an element of R. Prove u(x,y) + cv(x,y) is also harmonic.
I tried using the Laplace Equation of Uxx+Uyy=0
I have:
du/dx=Ux
d^2u/dx^2=Uxx
du/dy=Uy
d^2u/dy^2=Uyy
dv/dx=cVx
d^2v/dx^2=cVxx
dv/dy=cVy
d^2v/dy^2=cVyy
I'm not really sure how to...