Charge of a Sphere Physics?

Question

A sphere of radius 3 cm has an unknown amount of charge uniformly distributed over its volume. If the electric field at a distance 10 cm from the center of the sphere is 3 x10-3 N/C and points radially inward, what is the total charge on the sphere?

i'm trying to treat the sphere as a point charge, but i'm not getting a reasonable answer.

nm i got it

Answer 1

Hmmm...for charge uniformly distributed across a sphere you can indeed treat that as a point charge at the center of the sphere (proof by Gauss's Law). The charge is found using...

E = k q / r²

( 3 x 10^-3 N / C ) = ( 9 x 10^9 N m² / C² ) ( q ) / ( .10 m )²

I get about -3.3 x 10^-15 Coulombs (negative as the field is directed towards the sphere).

Answer 2

You are correct considering that the charged sphere behaves outside it as a point electric charge located at its center.
From Couilomb's formula in vaccum
E=q/4x3.14.epsilon(zero)rr
where q is the electric charge in As, r the distance from the center to the point where the electric field is measured in m and epsilon(0) the permitivity of empty space (you should look for a source of its value in IS units).

Answer 3

Are you remembering to handle the spheres as element fees? Then do your calculations based on the gap between centerpoints c1*c2 --------- (opposite signs and symptoms = internet charm) d^2 wish that enables

Answer 4

no fair...

I was going to devote my life to finding the answer for you and you went and figured it out!

so smarty pants whats the correct answer?

we're dying to know...