# Charge, before and after two touching objects.

1. Jan 19, 2014

### contrivance

1. The problem statement, all variables and given/known data

A plastic rod that has been charged to − 14nC touches a metal sphere. Afterward, the rod's charge is − 10nC . What kind of charged particle was transferred between the rod and the sphere, and in which direction? That is, did it move from the rod to the sphere or from the sphere to the rod?

[A] electrons, from the rod to the sphere
electrons, from the sphere to the rod
[D] protons, from the rod to the sphere
[D] protons, from the sphere to the rod

2. The attempt at a solution

I first picked B. My reasoning was since the rod started with -14nC, and the number increased to -10nC, this meant that it gained electrons.

Apparently the answer is A, it loses electrons.

This leads me to believe that I only have a half-understanding of what is happening with negative and positive charges. What am I missing?

2. Jan 19, 2014

### Simon Bridge

electrons are negatively charged ... if you gain electrons, you get more negative, or less positive.

the only charges that could move between the two solids is, of course, the electrons.

3. Jan 20, 2014

### contrivance

Thank you.

So that means an electron's charge is simply a property, and not a quantity, right? Now I realize that duh - you can't have a negative quantity of something.

4. Jan 20, 2014

### Simon Bridge

But you can have a negative quantity ... it's a negative quantity of charge, not a negative quantity of electrons.
You can have a negative quantity of electrons - that would involve removing electrons, which would make the charge less negative and more positive.