Question

Please help me guys.., (attachment)

Answer 1

what are r and sigma representing.

Answer 2

r is probably the vector from the origin to any point on the surface, and sigma is probably the unit vector normal to the surface at that point.

Answer 3

@CliffSedge can you help me please

Answer 4

Been too long since I've done integrals like these. I'll have to refresh my memory first.

Answer 5

So when it says that
\[ \vec{r}\cdot d\vec{\sigma}=0 \]
for three of the surfaces, can you see which three this pertains to and why?

Answer 6

why?

Answer 7

when, in general, is a dot product zero?