Question

A charged body has an electric flux $\phi$ associated with it. The body is now placed inside a metallic container. The flux $\phi$, outside the container will be
A. Zero
B. Equal to $\phi$
C. Greater than $\phi$
D. Less than $\phi$

Answer 1

Electric flux is the amount of electric field lines that pass through the given surface perpendicular to it. For anybody, the flux associated with it is the amount of field lines going out or coming into a surface.

Complete answer:
A metallic container will give rise to shielding of electric fields. Inside a metallic cavity the electric fields from the outside are completely shielded out and so are the electric fields from the inside. One can think of metallic containers as a kind of a wall or a barrier for an electric field. Therefore, as we place the charged body inside the metallic container its electric field will be completely shielded out by the metallic container and outside the metallic container we will observe no electric field coming out and hence there will be no flux outside of the metallic container even if a charged body is kept in it.

So, the correct answer is “Option A”.

Additional Information:
Due to the electric field of the body, charge gets induced on the inner and outer surface of the container creating an electric field of its own. So, what happens inside the metallic container is a charge gets induced such that it opposes the electric field of the charged body. This is how, the cancellation of the fields causes shielding due to metallic containers.

Note:
There is a condition involved here that the container and the charged body should not come in contact at any point else the charge will leak and the container will possess some charge which will lead to flux.