# Flux and Circulation

1. Aug 26, 2012

### 6.28318531

1. The problem statement, all variables and given/known data

Let F(x,y) = ( P(x,y), Q(x,y)) be a vector field that is continuously differentiable along the closed smooth curve C : x2+y2 = 1. Moreover let

-F(x,y) = F( -x, -y)≠ 0 and

P(x,y) = -P(-x,y) and Q(x,y) = Q(-x,y).

Determine all the possible values of the circulation around C, and argue why flux across C is non zero.

2. Relevant equations

Circulation = ∫CF. T ds , T tangent vector
Flux = ∫CF. N ds , N normal vector

3. The attempt at a solution

I'm not quite sure where to begin . Do we parametrize C by r(t) = (cos t, sin t) 0≤ t≤ 2$\pi$, and then use the definitions of flux and circulation?

2. Aug 26, 2012

### voko

From the given relations among F, P and Q you can deduce how they are related in all four quadrants. What will that mean with regard to the integrals?

3. Aug 26, 2012

### 6.28318531

Ah now I see for the flux part;

Look at each quadrant {x,y>0} {x,y<0} {x>0, y<0} and {x<0,y>0}

When x, y> 0, The integral evaluates to a value.

Let ∫CF.n ds = f

Then for x,y<0

the integral becomes ∫F( -P, -Q) .n ds = - f

Then for x> 0, y< 0
∫F(P(x,-y), Q(x,-y)).n ds= a ≠f

Then for x< 0, y> 0

∫F(P(-x,y),Q(-x,y)).n ds =∫ F( -P(x,y),Q(x,y)).n ds =b ≠a.

So you can see the total flux is non zero. The two regions x,y>0 and x,y<0 cancel out
and the other two are not equal.