Homework Help: A charged rod transfers electrons to a neutral conductor

1. Oct 7, 2011

RichardEpic

An initially neutral conductor contains a hollow cavity in which there is a + 65.0 nC point charge. A charged rod transfers - 75.0 nC to the conductor.

Afterwards, what are the charges along the inner surface and the exterior surface?

I understand that the charges from the rod are equally distributing itself across the
volumes, but I don't know how the numbers will play into this...at all. I do know that the
inner wall surface should be negative due to the 65nC point charge, and the outside must
be positive due to the fact that this is a neutral conductor.

ANY formulas dealing with this type of problem would be greatly appreciated!!!

2. Oct 7, 2011

WJSwanson

Remember that the charge distribution throughout a conductor will arrange itself according to two principles:

1. The charges will align such that there is no net electric field inside the conductor.
2. Any net charge will be stored on the outer surface of the conductor in a manner dependent on its geometry.

If you remember your equations for E and your conventions for electric-field lines, you should be able to solve the problem from there.

Last edited: Oct 8, 2011
3. Oct 8, 2011

RichardEpic

Ah, I think I'm understanding this now...I do know that the meat a conductor has an E-field of zero (E = 0). So, since the net charge only stays apparent on the exterior surface...would the interior surface charge stay the same? -65nC, in order to block the E-field of the +65nC point Charge?

Also, net charge on the surface should then be +65nC - 75nC = -10nC....correct?

THANK YOU!!! The world of Conductors has been made clearer to me! Answers were correct. :)

4. Oct 8, 2011

WJSwanson

Unless I missed something in the problem, you've got it, and yes, the net charge on that outer surface should be -10C. :)

5. Apr 9, 2013

Mandaz

correct me if i am wrong, since the hollow cavity of the conductor is +65, the wall of the hollow part of the conductor is -65, so it stay neutral and the outer surface of the conductor is also +65

if this is true hen way isn't inner wall of the hollow part -130

6. Apr 9, 2013

SammyS

Staff Emeritus
Do you realize that this is an old thread?

If a charge of -75 nC is transferred to a neutral object, the object will have a net charge of -75 nC after the transfer .

The electric field within the conducting material itself is zero, thus Gauss's Law tell us that the net charge on the inner surface (the surface of the cavity) must remain at -65 nC, the same as prior to the transfer.