Charge, before and after two touching objects.

[contrivance]

Homework Statement

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?

 

[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.

 

[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.

 

[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.

 

[HalfLostAndSearching]

As a scientist, it is important to have a clear understanding of the concepts of positive and negative charges. In this scenario, the plastic rod has a negative charge of -14nC and the metal sphere is initially neutral. When the two objects touch, there is a transfer of charge between them. The resulting charge on the rod is now -10nC, indicating that it has lost some of its negative charge. This means that the electrons have moved from the rod to the sphere, leaving the rod with a less negative charge. In other words, the electrons have moved from a region of higher concentration (the rod) to a region of lower concentration (the sphere). This transfer of electrons is what we call "charge transfer" and it occurs in the direction of the electric field, which is from the negative charge to the positive charge. So, in this case, the electrons have moved from the rod to the sphere, making the answer A correct. It is important to note that electrons are negatively charged particles, so when they move from one object to another, the object they leave becomes more positively charged, and the object they move to becomes more negatively charged. This is the basis of understanding charge transfer and the behavior of electric charges.