Calculating Wire Current and Electron Flow: A Helpful Guide | Thank-you

[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

 

[Doc Al]

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.

 

[hshphyss]

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

 

[Doc Al]

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.

 

[hshphyss]

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

 

[Doc Al]

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.)

 

[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?

 

[Doc Al]

Current = Charge/Time, or...

Charge = Current x Time.

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

 

[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?

 

[Doc Al]

yes... so its going to be current/time=charge

Nope. Reread what I wrote above.

 

[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

 

[Doc Al]

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).