Question

Compute the flux H F of F(x,y) = hxy, x − yi across the boundary of the square given by −1 ≤ x ≤ 1, −1 ≤ y ≤ 1.

Answer 1

Answer:

4i.

Step-by-step explanation:

To find the flux through the square, we use the divergence theorem for the flux. So Flux of F(x,y) = ∫∫divF(x,y).dA

F(x,y) = hxy,x - yi

div(F(x,y)) = dF(x,y)/dx + dF(x,y)dy = dhxy/dx + d(x - yi)/dy = hy - i

So, ∫∫divF(x,y).dA = ∫∫(hy - i).dA

= ∫∫(hy - i).dxdy

= ∫∫hydxdy - ∫∫idxdy

Since we are integrating along the boundary of the square given by −1 ≤ x ≤ 1, −1 ≤ y ≤ 1, then

∫∫divF(x,y).dA = ∫₋₁¹∫₋₁¹hydxdy - ∫₋₁¹∫₋₁¹idxdy

= h∫₋₁¹{y²/2}¹₋₁dx - i∫₋₁¹[y]₋₁¹dx

= h∫₋₁¹{1²/2 - (-1)/2²}dx - i∫₋₁¹[1 - (-1)]dx

= h∫₋₁¹{1/2 - 1)/2}dx - i∫₋₁¹[1 + 1)]dx

= 0 - i∫₋₁¹2dx

= - 2i[x]₋₁¹

= 2i[1 - (-1)]

= 2i[1 + 1]

= 2i(2)

= 4i