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mr_coffee
Oct16-05, 02:52 PM
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.

ZapperZ
Oct16-05, 02:56 PM
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.

mr_coffee
Oct16-05, 03:24 PM
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

ZapperZ
Oct16-05, 08:23 PM
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

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.