# Identical objects carry a net charge

1. Feb 3, 2014

### physicsSOS

1. The problem statement, all variables and given/known data
Each of the two identical objects carry a net charge. The objects are made of conducting material. One of them is attracted to a positively charged ebonite rod, and the other is repelled by the rod. After the objects are touched together, it is found that they are each repelled by the rod. What can be concluded about the initial charges on the objects?

a) initially, both objects are positive, with both charges having the same magnitude.
b) Initially both objects are negative, with both charges having the same magnitude.
c) Initially one object is positive and one is negative, with the positive charge having a greater magnitude than the negative charge.
d) Initially one object is positive and one is negative, with the negative charge having a greater magnitude than the positive charge.

2. Relevant equations
E(r)=k*Q/r^2

F=k*lQ1l * lQ2l / r^2 [the bars are supposed to represent the magnitude]

3. The attempt at a solution
The answer is c). Could you please explain thoroughly (but in simple words if possible) why that is the case, and why it's the positive charge that has to have a greater magnitude and not the negative?
Also, what difference would it make if the objects were made of insulating material?

2. Feb 3, 2014

### jackarms

You know that they are of opposite charges, since one is attracted to the rod and the other is repelled. After touching, they are both repelled, so that means both are positive in the end. Since they were of opposite charges to start, the positive charge has to "win" over negative during the transfer.