Is Solving Laplace's Equation for a Dielectric Cylinder Straightforward?

In summary, the conversation discusses solving Laplace's equation to find the electric potential in a hollow dielectric cylinder with a given boundary condition. The process involves finding series solutions in the appropriate coordinate system and using separability to solve for the undetermined coefficients. The conversation also mentions the use of spherical and cylindrical harmonics in cylindrical coordinates. There is also a mention of a non-linear second order partial differential equation for the radius function, which may not be correct.
  • #1
Sam2000009
OP warned about not using the homework template
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 into (del)^2 u where u=v?

I did that but it seems too simplistic
 
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  • #2
The surface of the cylinder is a boundary condition. Typically you will want to find the series of solutions to Laplace's equation in the appropriate coordinate system to the problem at hand. (Here I would guess cylindrical coordinates). There will be an infinite series of undetermined coefficients which must be chosen to match the boundary conditions.

Since Laplace's equation is a linear equation and here it is homogeneous (away from the boundary) so any linear combination of solutions is again a solution. The trick is finding those and then finding the right linear combination to match the boundary conditions.

Some details. You should be able, with a quick search, to find Laplace's equation in various coordinate systems. You then assume separability and solve.
In cylindrical coordinates you have... well just see the Wikipedia and/or Wolfram MathWorld pages on spherical harmonics and cylindrical harmonics.
 
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  • #3
I did all that and a got a messy non linear second order partial differential equation for the r function (radius) which I am pretty sure is not right
 
  • #4
Sam2000009 said:
I did that but it seems too simplistic.
You mean "too simple." Simplistic means "oversimplified," and it doesn't really make sense to say something is "too simplistic" because there's no right level of oversimplification. If a situation were simplified the right amount, it wouldn't be oversimplified, would it?

Sam2000009 said:
I did all that and a got a messy non-linear second-order partial differential equation for the r function (radius) which I'm pretty sure is not right.
Telling us you tried something and got the wrong answer isn't very helpful. We need to see what you did to be able to give advice. Please post your work if you want help.
 
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1. What is the Laplace equation?

The Laplace equation, also known as the second-order partial differential equation, is a mathematical equation used to describe the steady-state temperature distribution in a given region with specified boundary conditions. It is named after French mathematician and astronomer Pierre-Simon Laplace.

2. What are the applications of the Laplace equation?

The Laplace equation has various applications in fields such as physics, engineering, and mathematics. It is used to solve problems related to heat conduction, electrostatics, fluid flow, and potential theory.

3. How is the Laplace equation solved?

The Laplace equation can be solved using various techniques such as separation of variables, Fourier series, and Green's function. The appropriate method depends on the boundary conditions and the geometry of the problem.

4. What are the boundary conditions for solving the Laplace equation?

The boundary conditions for solving the Laplace equation vary depending on the specific problem. However, in general, the boundary conditions include specifying the temperature or potential at the boundaries of the region, which are often referred to as Dirichlet boundary conditions, or specifying the normal derivative of temperature or potential, known as Neumann boundary conditions.

5. What is the difference between the Laplace equation and the Poisson equation?

The Laplace equation and the Poisson equation are closely related, but there is a key difference. The Laplace equation describes the steady-state temperature or potential distribution in a region, while the Poisson equation includes a source term and is used to describe the distribution in the presence of sources or sinks of heat or charge.

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