 #1
archaic
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 210
 Homework Statement:

We have a thin spherical shell with a spherically symmetric negative charge distribution inside. The radius of the shell is ##R=0.705\,m##, and the electric field strength at its surface is ##E=867\,N/C## everywhere, and is pointing radially toward the center of the sphere.
What is the net charge within the sphere's surface?
 Relevant Equations:
 .
The electric field caused by the surface distribution on a point ##a## meters far from it is$$E(a)=\frac{kQ}{(R+a)^2}$$from which I get$$Q=\frac{(R+a)^2E(a)}{k}=\frac{(R)^2E(0)}{k}=\frac{(0.705)^2\times867}{8.99\times10^9}\approx4.79\times10^{8}$$and I take its negative because the direction of the field is inwards.
I'm being told that this is wrong, though. Have I misunderstood the question, or approached it incorrectly?
I'm being told that this is wrong, though. Have I misunderstood the question, or approached it incorrectly?