# Point charge inside a electrically neutral cavity in conduct

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1. Dec 21, 2015

### ELiT.Maxwell

bear with me, i know that this question has been asked many time , but i would like a definite answer, now, starting off the external charge density on the outer surface of sphere WILL be uniform by unique solution of Laplace equation and letting the sphere be huge, so, electric field due to outer surface charge=0, now, we come to the inner surface, where, if the charge was placed eccentrically then, there would be more induced charge of opposite polarity near the real charge if we chose sphere as cavity to cancel out the electric field of real charge so there MUST be NET force on the charge due to the internal cavity surface charge. -> right?

• if there was external electric field then the outer surface would cancel out the electric field inside the conductor at ALL the points again by unique solution if we let the cavity be very small hence, the answer shouldnt change-> right?
can somebody atleast tell me the exact answers of these questions and if my approach of using induced charges due the chrage itself to calculate force on itself is correct or not.. (dont be mislead by real charge...by it i mean the charge WE placed inside it)

extra if anybody has extra time- electric field inside cavity will be vector sum of the induced and real charge is there an image method for it?

2. Dec 21, 2015

### LunaFly

3. Dec 22, 2015

### ELiT.Maxwell

i have done those questions where we need to calulate electric field due to charge in cavity etc and all the things related to multiple charges at centre of multiple spherical cavities, and know how to use gauss law and things related to conductor, according to griffeth, and using the uniqueness theorem, the outer surface charge is uniform or it would be anything to cancel out the outside electric field so,no net effect of outside, now on the inside surface where -q was induced, and the q itself MUST cancel out in the thickness of conductor so, since the q is nearer to a surface more charge density should be there and since the charge is of opposite polarity, it must attract it and the charge should be absorbed by the conductor -> any mistakes?