# What is the net charge

1. Jan 8, 2008

### rcmango

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

A metal sphere has a charge of +7.0 µC. What is the net charge after 8.00 10^13 electrons have been placed on it?
in µC

2. Relevant equations

3. The attempt at a solution

I believe that the charge of an electron is: -1.6 x 10^-19 C
and there are 8 electrons,

so -1.6 x 10^19 C * 8.00 x 10 ^13 electrons right?

then I add it to 7 uC? well i'm having trouble with the sigfigs, I got 5.72 uC I don't believe that is correct.

2. Jan 8, 2008

### Mindscrape

Do you have a rounding error? I am getting -5.8µC.

3. Jan 8, 2008

### rcmango

ah, I see from your answer. Sometimes it just takes someone else.

it was my sign! it has to be negative.

Thankyou!

4. Jan 8, 2008

### rcmango

also, when i get the answer, after multiplying the electrons, does +7.0 uC have sigfigs? i can't seem to figure out why my calculater won't give me anything past 1.28 x 10^33 i believe.

5. Jan 8, 2008

### Mindscrape

Sorry I don't understand your calculator comment. 7.0µC has 2 significant figures, and it means $7.0*10^{-6}$C. 7.00µC would be 3 sig figs, and 7µC would be 1 sig fig.