1. gerryliyana Group Title

2. Algebraic! Group Title

what are r and sigma representing.

3. Carl_Pham Group Title

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.

4. gerryliyana Group Title

@CliffSedge can you help me please

5. CliffSedge Group Title

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

6. Jemurray3 Group Title

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7. Jemurray3 Group Title

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8. Jemurray3 Group Title

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?

9. gerryliyana Group Title

why?

10. Jemurray3 Group Title

when, in general, is a dot product zero?