# What is actually being removed when a metal conductor is grounded?

I found this image earlier this morning, and yes, there are a lot of diagrams/illustrations about this, transferring charges by induction has been introduced since the very beginning of high school and is very straightforward.

But I noticed something odd about these illustrations, it is said that if, in this case, a sphere has excess positively charged particles, the earth would try neutralizing it by sending electrons (negative charges), but in figure $$(a)$$ the amount of positive and negative charges are equal ($$3+$$ and $$3-$$), so where are these called excess charges, if the metal sphere/conductor is completely neutral?

Any response would be very helpful!

• You may be confusing "grounded" (at zero potential) with "neutral" (with zero charge).
– user137289
Commented Aug 4, 2019 at 16:51

## 2 Answers

Without using the idea of potential it is difficult to explain – without a lot of hand-waving – why electrons move from Earth to the sphere in step (b).

Using the idea of potential it is very easy... In step (a) the charge separation on the sphere stops when all the sphere is at the same potential. This potential will be positive because the sphere is in the vicinity of the positively charged rod. Therefore electrons will flow from Earth to the sphere in step (b), because negative charges will flow from a lower potential to a higher potential.

I'm sorry if you have not yet learned about potential. It's not an especially difficult idea, but it needs (in my opinion) to be taught slowly and carefully, so I'm not attempting to teach it in this answer.

This is charging by induction, here is what is going on in each figure.

a) The positive charges on the rod repel the ones on the sphere, so a charge separation occurs. Note that the sphere has remained neutral.

b) The sphere is grounded, meaning it is connected to the earth. The earth can readily accept or give electrons. Here it sends electrons.

c) Because the earth sent electrons, the positive charges that were in figure a and b have now been neutralized by the electrons of the earth. Now the sphere is not neutral, it has a net negative charge.

d) The rod is removed from the system. Now the sphere is charged. Because the rod never came in contact with the sphere, we call this charging by induction.