Question

Find the net electric flux through the spherical closed surface shown in the figure below. The two charges on the right are inside the spherical surface. (Take q1 = +1.84 nC, q2 = +1.02 nC, and q3 = -2.91 nC.)
N · m2/C

Answer 1

By Gauss' theorem, the flux through a Gaussian surface is equal to the sum of the charges inside the surface scaled by 1/4.pi.e0.

use that result.

Answer 2

so (Q2+Q3)1/4.pi.e0?

Answer 3

they're the only charges in the surface, yes. I strongly recommend you watch the lecture I just linked in your other question.

Answer 4

**correction: no 4.pi. That goes away in the integration.

Answer 5

i was wondering why i was getting the wrong answer lol

Answer 6

You know you're in danger in Physics when you're using equations and you don't know where they come from.

Use that rule to be intellectually honest with yourself: what is this equation, where did come from, what does it mean physically, can I derive it from first principles in physics?

Answer 7

hmm... so I'm getting ((1.02x10^9)-(-2.91x10^9)/8.85x10^12=-2.14x10^-20
?? that doesn't seem right

Answer 8

That's not the value of the permittivity in a vacuum.

http://en.wikipedia.org/wiki/Vacuum_permittivity

Answer 9

oops.. i had put -12 in the calculator.. but not on here. my bad.

Answer 10

Also the charges are in nano Coulomb, not giga Coulomb !

-9, not +9

Answer 11

god.. i hate stupid mistakes. lol