# Homework Help: Electric Current - Finding # of Electrons

1. Mar 2, 2009

### calvert11

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

a) The potential difference in a simple circuit is 13 V and the resistance is 3 . What current I flows in the circuit? Answer in units of A.

(I got I = 4.333 which is correct)

b) How many electrons pass a given point in the circuit in 7 min?

2. Relevant equations

I=$$\Delta$$Q/$$\Delta$$t
n = I*t/q

3. The attempt at a solution
I'm having trouble with Part B of the question.

I used n = I*t/q, so 4.333A*420sec/1.6e^-19 = 1.1374e^22

Also, one ampere is 1 C per second, so 4.333*6.241e^18*420sec = 1.1357e^22

2. Mar 2, 2009

### Delphi51

The first method looks good to me. (I'm not familiar with the mole of electrons approach.)
Could it be a significant digits problem? The given numbers suggest rounding to 1 or 2 digits. If you want 5 digits, better find a more accurate value for e.

3. Mar 2, 2009

### calvert11

Sigfigs aren't checked. But generally, the more digits the better.

Other than that, you don't see anything wrong with my answer?

4. Mar 2, 2009