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Homework Help: Verify Stokes' theorem

  1. Jan 13, 2015 #1
    1. The problem statement, all variables and given/known data
    Verify Stokes' theorem for the following:

    [itex]F=[y^2, x^2, -x+z][/itex]

    Around the triangle with vertices [itex](0,0,1),(1,0,1),(1,1,1)[/itex]

    2. Relevant equations
    [itex]\int\int_S(curlF)\cdot ndA=\int_C F\cdot r' ds[/itex]

    3. The attempt at a solution

    For the LHS:
    [itex]curlF\cdot n=2x-2y[/itex]
    [itex]\int\int_S(curlF)\cdot ndA=\int_0^1 \int_0^{1-x}2x-2ydydx [/itex]

    This gives zero. Also integrating over the three curves of the triangle gives zero. However, the book's answer is 1/3. Any idea what the mistake is?
  2. jcsd
  3. Jan 13, 2015 #2


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    First of all, the area of integration is wrong. The triangle is bounded by the line x = y, the x axis, and the line y = 1.

    Second, in this area, the integrand is 2x - 2y = 2(x-y). For the entire area, this is positive (except for at the boundary x = y, where it is zero). The result must therefore be positive. Try drawing the points (in the x-y-plane, the z-coordinate is constant) on a piece of paper. In the region you have integrated over, the integrand is antisymmetric with respect to x=y and the the area is symmetric with respect to this and should therefore give a zero result.

    In short, you have verified Stokes' theorem, but for a different curve.
  4. Jan 14, 2015 #3
    Thank you, stupid me.
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