Exercises

1) Graph the cylinder x^2 + y^2 = 1and the hyperbolic paraboloid z = y^2 - x^2on the same set of axes, and parametrize the curve C where they intersect.  Verify Stokes's Theorem for the vector field F(x,y,z)=(x^2y, 1/3x^3, xy) and the curve C.  [i.e. Show that the line integral of F along C equals the appropriate surface integral.  You will need to produce your own surface.]

2) Now consider the vector field F(x,y,z)=(x^2y, x, xy).
a) Calculate the line integral of F along the circle parametrized by f_1(t) = (cos(t), sin(t), 1), for 0<t<2π .
b) Calculate the line integral of F along the circle parametrized by f_2(t) = (cos(t), sin(t), 0), for 0<t<2π .
c) Calculate the surface integral of curl(F) over the surface parametrized by g(s,t)=(cos(t),sin(t),s), for 0<t<2 π and 0<s<1.
d) Explain your answers in terms of Stokes's Theorem.

3) Use Stokes's Theorem to evaluate the line integral of the vector field F(x,y,z)=(y + sin(x), z^2 + cos(y), x^3), where C is the curve parametrized by f(t)=(sin t, cos t, sin(2t)), for 0≤t≤2π.

4) Consider the vector field G(x,y,z)=(x,y,z).  Use Stokes's Theorem to prove, by contradiction, that G is not the curl of any smooth vector field F.  [Hint: Let M be the unit sphere centered at the origin. The path integral over ∂M of every smooth vector field F equals 0 -- explain why!]

Credits

This lab was written  by James Swenson in 2002.  In Spring 2004 Jonathan Rogness went through and updated a few minor things to reflect the use of our math2374.nb file.

This lab is copyright 2002 by James Swenson (swenson@math.umn.edu) and is protected by the Creative Commons Attribution-NonCommercial-ShareAlike License.  You can find more information on this license at http://creativecommons.org/licenses/by-nc-sa/1.0/.

Although it's not specifically required by the license, I'd appreciate it if you let me know at rogness@math.umn.edu if you use parts of our labs, just so I can keep track of it.  Please send me any questions or comments!


Created by Mathematica  (November 22, 2004)