# Homework Help: Electricity - Charges

1. Jun 23, 2008

### ital_dj

1. The problem statement, all variables and given/known data
If an electroscope has a positive charge of 7.5 x 10$$^{-11}$$C, how many electrons have been removed from the electroscope, if it was originally neutral?

(Answer: 4.7 x 10$$^{8}$$)

2. Relevant equations
I don't know :shy:

3. The attempt at a solution
Guys I seriously am clueless with this question. I understand basic electricity a little, like circuits, but I don't even know where to start with this. I have all formulas required, but I don't know which one to use, and my exam is tomorrow :uhh:

There are also some other questions which I'll probably post later, I'm really stuck on this, and your help is appreciated... a lot!

Thanks

2. Jun 23, 2008

### Redbelly98

Staff Emeritus
What is the charge of a single electron?

3. Jun 23, 2008

### ital_dj

-1?? I don't know to be honest with you.

4. Jun 23, 2008

### rock.freak667

an electron has a charge of $-1.6 \times 10^{-19}$

5. Jun 23, 2008

### ital_dj

Okay, thanks.. but how do I put that into the question??

6. Jun 23, 2008

### rock.freak667

The charge on the scope= Ne
where N=No of electons and e=charge on one electron

7. Jun 23, 2008

### ital_dj

well... what you told me is like a completely new language to me... thanks for the help, but i really don't understand it (i understand what you're saying but i don't know what to do with that)... is there a specific equation i can use?

EDIT: I'm going to bed, my exam's early in the morning... I guess electricity won't be that great on the exam. Thanks everyone for the help.

Last edited: Jun 23, 2008
8. Jun 24, 2008

### Redbelly98

Staff Emeritus
It might have been beneficial to include units (Coulombs) in that answer, but anyway it's a moot point now.

9. Jun 24, 2008

### ital_dj

Well I did the exam today so i'm done with physics for now... no need for the answer... I think I did pretty decent on the exam... no questions like that, though.

Thanks everyone for the help.

10. Jun 24, 2008

### Gear300

well...at least everything well

11. Jun 24, 2008

### rock.freak667

Even though it's up to you to want to know the answer, IMO it's best to understand how to get the answer so in case you are presented with a similar question,you'd know how to get through it.