Laplace Equation Solution

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Questions and Answers

Which method is most suitable for solving the given Laplace equation with a source term and zero boundary conditions on a square?

  • Direct integration
  • Finite element method
  • Using Green's functions
  • Separation of variables with Fourier series expansion (correct)

Given the equation $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ and assuming a solution of the form $u(x, y) = \sum_{m=1}^{\infty} \sum_{n=1}^{\infty} A_{mn}sin(mx)sin(ny)$, what equation must $A_{mn}$ satisfy?

  • $(-4 - 3m^2 - n^2)A_{mn} + \int_{0}^{\pi} \int_{0}^{\pi} sin(2x) dxdy = 0$
  • $(-4 + 3m^2 + n^2)A_{mn} = 0$
  • $(-4 - 3m^2 - n^2)A_{mn} + \int_{0}^{\pi} \int_{0}^{\pi} sin(2x)sin(mx)sin(ny) dxdy = 0$ (correct)
  • $(-4 - 3m^2 - n^2)A_{mn} = 0$

In solving $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ with $u(x, y) = \sum_{m=1}^{\infty} \sum_{n=1}^{\infty} A_{mn}sin(mx)sin(ny)$, for what values of $m$ and $n$ will $\int_{0}^{\pi} sin(2x)sin(mx) dx$ be non-zero?

  • For all integer values of $m$
  • Only when $n = 0$
  • Only when $m = 0$
  • Only when $m = 2$ (correct)

Given the equation $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ with zero boundary conditions, and the solution form $u(x, y) = \sum_{m=1}^{\infty} \sum_{n=1}^{\infty} A_{mn}sin(mx)sin(ny)$, which expression correctly describes $A_{2n}$?

<p>$A_{2n} = \frac{\frac{4}{\pi^2} \int_{0}^{\pi} \int_{0}^{\pi} sin(2x)sin(2x)sin(ny)sin(ny) dxdy}{(-4 - 12 - n^2)}$ (D)</p> Signup and view all the answers

If the solution to $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ is given by $u(x, y) = \sum_{n=1}^{\infty} A_{2n}sin(2x)sin(ny)$ and $A_{2n} = \frac{c}{(-16 - n^2)}$, what happens to the amplitude of higher modes as n increases?

<p>The amplitude of higher modes decreases quadratically. (A)</p> Signup and view all the answers

Flashcards

Laplace Equation

A second-order partial differential equation that describes the steady-state distribution of a potential, such as temperature or voltage.

Solution to Laplace Equation

A function, u(x,y), whose Laplacian (sum of second-order partial derivatives) equals zero.

Boundary Conditions

Conditions specifying the value of the unknown function on the boundary of the domain.

Given Problem

A problem solving $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ on a square $0 < x, y < \pi$ subject to zero boundary conditions.

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Particular Solution

In this case, it will be a function u(x,y) that satisfies both the equation $-4u + 3u_{xx} + u_{yy} + sin(2x) = 0$ and the condition u = 0 on all sides of the square.

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Study Notes

  • The task is to solve the Laplace equation: -4u + 3u_xx + u_yy + sin(2x) = 0
  • The equation needs to be solved on a square where 0 < x, y < π.
  • The boundary conditions are zero, meaning u = 0 on the top, bottom, left, and right sides of the square.

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