2nd order diff eq, 3 dim. and wierd boundry condition

In summary, the conversation discusses solving for a scalar field inside a box using a differential equation. The field is described by a Helmholtz equation and has specific boundary conditions. The conversation also mentions using separation of variables to solve the equation. The final solution should be an analytic expression. The individual asking for help is unsure how to solve the equation since it is not a traditional wave equation.
  • #1
johnnymopo
2
0
I need help. For the following problem, can someone suggest how I should start on this question. I only have one quarter of diff eq classes plus a few classes in Fourier analysis. I'm out of my league.

Consider a box with length, width and height given by L. The box encompasses the region
described by 0<=x<=L, 0<=y<=L, and 0<=z<=L. A scalar field inside the box satisfies the
differential equation:

∇^2 ψ = −aψ

Here a is a positive constant that is equal to 30/L2.
The field is 0 on the surfaces y=0, y=L, x=0, x=L and finally the surface z=L.
On the surface z=0, the field has the functional form:

ψ(x, y) = ( 1-|x-2/L|*2/L)(1- |x-2/L|*2/L)

Solve for ψ as a function of x, y, and z inside the box. Your final solution must be
an analytic expression, though it can involve an infinite sum.


What I don't understand is that ψ is time-independant wave, correct? and if so, how do I solve this when the boundry on one face is clearly not a wave. Please point me in the right direction to figure out how to do this. thanks.
 
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  • #2


Well, this isn't a wave equation since it doesn't involve t.

Have you tried separation of variables: [itex]\Psi(x,y,z) = X(x)Y(y)Z(z)[/itex]?
 
  • #3
Is that not a Helmholtz equation, and is a Helmholtz not a time-independant wave?
 
  • #4
johnnymopo said:
Is that not a Helmholtz equation, and is a Helmholtz not a time-independant wave?

Yes it is. And apparently it is referred to as a wave equation.
 

1. What is a 2nd order differential equation?

A 2nd order differential equation is an equation that involves the second derivative of a function. It is commonly used in scientific research to model the behavior of systems and processes.

2. How does a 2nd order differential equation relate to 3 dimensions?

In 3-dimensional space, a 2nd order differential equation involves two independent variables and their corresponding derivatives. This allows for more complex and accurate modeling of physical systems.

3. What are some examples of weird boundary conditions?

Weird boundary conditions are conditions that are not commonly encountered in typical mathematical problems. Some examples include non-linear boundary conditions, discontinuous boundary conditions, and boundary conditions involving complex functions.

4. How are 2nd order differential equations solved?

There are various methods for solving 2nd order differential equations, including separation of variables, variation of parameters, and Laplace transforms. The appropriate method depends on the specific equation and its boundary conditions.

5. How are 2nd order differential equations used in scientific research?

2nd order differential equations are commonly used in scientific research to model the behavior of physical systems and processes. They can help predict the future behavior of a system based on its current state and external factors, and can also provide insights into the underlying mechanisms driving the system's behavior.

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