# Electric Current Help

1. Jan 18, 2006

### hshphyss

Can anyone help me with this question? Thank-you

A net charge of 51 mC passes through the cross-sectional area of a wire in 10.0 s. What is the current in the wire? How many electrons pass the cross-sectional area in 1.0 min?

I know that the current is .0051, but I'm having trouble finding the electrons. I know an amp is a coulomb per second, am I going to use C=6.3e18 somewhere? I tried 6.3e18/60 sec but that was wrong

2. Jan 18, 2006

### Staff: Mentor

Hint: The charge on an electron is 1.6e-19 C. (6.25e18 is the number of electrons required to make one Coulomb of charge.) Start by figuring out how much charge (in Coulombs) passes in 1.0 min.

3. Jan 18, 2006

### hshphyss

would i multiply 1.6e-19 C x 60 seconds? I have to use seconds correct?

4. Jan 18, 2006

### Staff: Mentor

No. You found the current (0.0051 A) so use it. Current = charge/time; you have the current and the time: solve for the charge. Then figure out how many electrons equal that charge.

5. Jan 18, 2006

### hshphyss

I get 1.36e-5 for the charge. So is it going to be 1.36e-5/1.6e-19?

6. Jan 18, 2006

### Staff: Mentor

How did you get that value for the charge? (Once you get the correct charge, yes, divide it by the electron charge to find the number of electrons.)

7. Jan 18, 2006

### hshphyss

i divided the current by 60 seconds... .0051/60 then i multiplied it by 1.6e-19 and i got 8.5e-5, but that is wrong what did i do?

8. Jan 18, 2006

### Staff: Mentor

Current = Charge/Time, or...

Charge = Current x Time.

(If you keep track of your units, you'll make fewer mistakes.)

9. Jan 18, 2006

### hshphyss

yes... so its going to be current/time=charge and i got 8.5e-5 then i multiplied it by the charge on an electron 8.5e-5 x 1.6e-19 and I got 1.36e-23. Where am i going wrong?

10. Jan 18, 2006

### Staff: Mentor

Nope. Reread what I wrote above.

11. Jan 18, 2006

### hshphyss

my apologies after i multiplied current x time i got 0.306, and then I divide by 1.6e-19? I want to make sure I get this right becausr I am running out my submissions, thank-you for ur time

12. Jan 19, 2006

### Staff: Mentor

Correct. But always attach units to your answers. When you multiplied current by time you got charge, so that answer was 0.306 C. And you will divide by 1.6e-19 C per electron. Your final answer will be just a number (of electrons).