# Physics Question

1. May 11, 2005

### Jodi

Hi; Could somebody please help me with this question: A 3.0g copper penny has a postive charge of 38uC. What fraction of its electrons has it lost?
The method I tried was: (3g/63.55g) x 6.02E23 x A(what i'm solving for) = 38xE-6. Than I took my answer and divided it by 29. However this will not give me the correct answer, and the correct answer is 1/(3.5E9). Can somebody please help me. Thank you so much.

2. May 11, 2005

### StatusX

Look at your units. You have a dimensionless number on the left side and coulombs on the right side. You need to factor in the charge on an electron.

3. May 11, 2005

### rune

Try a more systematic approach:

- How many electrons does it take to make up $$-38\mbox{\mu C}$$ charge? (hint: use the electron charge)

- How many electrons are in 3.0g copper (when neutral)? (29 per copper atom)

4. May 11, 2005

### Jodi

Thanks...

Thanks guys, I figured this one out.