# Homework Help: At what rate do electrons flow through any cross section

1. Oct 16, 2005

### mr_coffee

I got the first part of this question but can't seem to get the 2nd part..
A 105 V potential difference is applied to a space heater that dissipates 1000 W during operation.

(a) What is its resistance during operation?
11.025 OHM
(b) At what rate do electrons flow through any cross section of the heater element?
wrong check mark s-1

Well that sounds like they want me to find the current, so i tried
$$P = i^2R$$
$$i = sqrt((1000/11.025))$$;
i = 9.5238;
I submitted it konwing it would be wrong, because it said it wanted section s^-1. So i tried 1/i = .105, which is s, which was wrong, any ideas\? Thanks.

2. Oct 16, 2005

### ZapperZ

Staff Emeritus
Current is amount of charge flowing through an area per unit time. So this is rate of CHARGE FLOW, i.e. Q/time. Your question asked for rate of ELECTRON flow, which is number/time.

Since you already found Q/time, and you know how much charge each electron has, shouldn't it be rather straightforward to find out how many electrons actually flow across an area per unit time?

Zz.

3. Oct 16, 2005

### mr_coffee

OKay i think i got it, but the answer is so small i'm thinking its wrong how i did it...
If i'm trying to find what rate electrons flow thorugh any cross section of the heater element, I need to find # of electrons/time, like you said..
So:
#(1.68E-19)/seconds * (1 second/9.5238A) = 1.680E-20;
but that leaves me with CA, which isn't right...
I also tried 1.68E-19*9.5238

4. Oct 16, 2005

### ZapperZ

Staff Emeritus
What did you do here?

You have current in x Amp., which is in units of coulombs/second. So

x C/s * 1e/1.6E-19C = #e/s

I believe this is a VERY large number.

Zz.