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

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
3 replies · 2K views
johnnymopo
Messages
2
Reaction score
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-independent wave, correct? and if so, how do I solve this when the boundary on one face is clearly not a wave. Please point me in the right direction to figure out how to do this. thanks.
 
Physics news on Phys.org
Is that not a Helmholtz equation, and is a Helmholtz not a time-independent wave?