# Circulation

• June 8th 2009, 09:48 AM
Apprentice123
Circulation
Determine the circulation of $F(x,y,z) = (z-x)i +(x-y)j + (e^{xyz})k$ around the curve $\alpha$ traveled in a counter-clockwise direction when viewed from the axis OZ, knowing that this curve is the edge of the surface: S1 $x^2+y^2+z^2 = 4; z > 0$
• June 8th 2009, 11:03 AM
Calculus26
Disregard this attachment

See correct version on later post
• June 8th 2009, 11:05 AM
Random Variable
EDIT: fixed errors

$\int \int_{S} curl F \cdot dS = \int_{C} F \cdot dr$

I think they mean that the boundary curve is $x^{2}+y^{2} = 4$

which can be parametrized by $r(\theta) = 2cos(\theta) \hat{i} + 2sin(\theta) \hat{j} + 0 \hat{k}$

where $0 \le \theta \le 2 \pi$

then $\int_{C} F \cdot dr = \int_{0}^{2 \pi} F(r(\theta)) \cdot r'(\theta) \ d \theta$

where $F(r(t)) = -2cos(\theta) \hat{i} + 2\big(cos(\theta) -sin (\theta)\big) \hat{j}+ \hat{k}$

and $r'(t) = -2sin(\theta) \hat{i} + 2cos(\theta) \hat{j} + 0 \hat{k}$
• June 8th 2009, 11:13 AM
Apprentice123
Quote:

Originally Posted by Random Variable
EDIT: fixed errors

$\int \int_{S} curl F \cdot dS = \int_{C} F \cdot dr$

I think they mean that the boundary curve is $x^{2}+y^{2} = 4$

which can be parametrized by $r(t) = 2cos(\theta) \hat{i} + 2sin(\theta) \hat{j} + 0 \hat{k}$

where $0 \le \theta \le 2 \pi$

then $\int_{C} F \cdot dr = \int_{0}^{2 \pi} F(r(\theta)) \cdot r'(\theta) \ d \theta$

where $F(r(t)) = -2cos(\theta) \hat{i} + 2\big(cos(\theta) -sin (\theta)\big) \hat{j}+ \hat{k}$

and $r'(t) = -2sin(\theta) \hat{i} + 2cos(\theta) \hat{j} + 0 \hat{k}$

How you found $F(r(t))$ ?
• June 8th 2009, 11:21 AM
Random Variable
Quote:

Originally Posted by Apprentice123
How you found $F(r(t))$ ?

$r(\theta)$ can be written as

$x = 2cos(\theta)$
$y = 2sin(\theta)$
$z = 0$

Do you know the final answer? I get $4 \pi$
• June 8th 2009, 11:34 AM
Calculus26
Verification with Stokes Thm

previous post corrected

See attachment
• June 8th 2009, 11:48 AM
Apprentice123
$4 \pi$ thanks