# E=0 inside the conducting sphere Always?

1. Nov 25, 2015

### gracy

An uncharged metal sphere suspended by a silk thread is placed in a uniform external electric field E.(a)What is the magnitude of the electric field of points inside the sphere?(b)Is your answer changed if the sphere carries a charge?
I would have asked this in homework forum but it does not involve any calculations and I have also been provided with it's answer ,I am just going to ask a conceptual question based on the answer

Answer:(a)$E$=0
(b)
No
As we can see there is silk thread then there is external field to confuse the student that there is a special kind o set up hence there can be $E$≠0 inside the metallic/conducting sphere but the answer is as usual $E$=0 So it Does it mean $E$=0 inside the metallic/conducting sphere no matter what.
Or are there any examples any set up any situation where $E$≠0 inside the metallic/conducting sphere

2. Nov 25, 2015

### .Scott

For the most part, it does not matter. The metal sphere shields the interior from external electromagnetic forces - acting as a Faraday cage.

There are extreme cases. If you suddenly deposit a charge onto one spot on the sphere, that charge will move across the surface of the sphere at almost the speed of light. During that short time, the interior of the sphere will be exposed to a non-uniform electric field.

If a voltage can be maintained across the surface of the metal sphere, a charge could be induced. It the "metal" is not superconducting, this could be done by putting a current through the ball and counting on the resistance to create the voltage.

Also, a voltage can be induced with a strong magnetic field.

But, for normal situation and for common purposes, the charge will remain uniform.

3. Nov 25, 2015

### Staff: Mentor

E=0 is guaranteed inside a conductor only in the electrostatic case. In cases where there are currents or changing fields then there may be E fields inside a conductor.

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