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archaic

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- 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?