Given this picture, I've understood that giver r>R, E = q/(4πεR^2) but I just can't get why inside the sphere, E equals 0? And the notes don't explain something. I've tried to look it up on the web and found similar examples that don't explain it either...
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$\begingroup$ For the exact same reason there is no gravity inside the Earth. $\endgroup$– Ryan UngerFeb 3, 2015 at 10:44
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1$\begingroup$ possible duplicate of Inside a conductor? $\endgroup$– John RennieFeb 3, 2015 at 10:51
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1$\begingroup$ 0celo7: the only place inside the Earth where the gravity is zero is at the centre. By contrast the field is zero everywhere inside a conductor. $\endgroup$– John RennieFeb 3, 2015 at 10:53
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$\begingroup$ @JohnRennie: I should have said hollow sphere, correct? My bad. $\endgroup$– Ryan UngerFeb 3, 2015 at 12:00
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$\begingroup$ @0celo7: well yes, there is no gravity inside a hollow shell, but the OP is asking about a solid conductor not a hollow one (or at least they don't specifically say it's hollow). $\endgroup$– John RennieFeb 3, 2015 at 12:02
1 Answer
First, the context is electrostatics so we assume the net force on any charged particle is zero; if the net force is not zero, the charged particle will accelerate and the situation would not be static.
Inside a conductor, by definition, charge is free to move; if there is an electric field inside, charge will be accelerated.
Thus, we must conclude that, in the electrostatic case, there is no electric field inside a conductor.
Put another way, if there is an electric field inside, it is not the electrostatic case.