Quote:
Originally posted by Avatar:
Kaz:
I'm doing Electronic Engineering at Cambridge 1st year:
R changes ONLY with material, temperature, length and area.
I think  I ought to know...
Voltage (potential difference) is adjustable and the current THROUGH the resistor changes acoordingly. THE REISITOR can heat up as a result of this...
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Hello fellow Electronic Engineer (I supposed to do second year, but I delayed for a half year).
Anyways, Rikard, that is NOT right what you've said about U/I = l/A. Kaz, forget that, not right!!
About your problem with the calculations, I did the calculation as well, this is how it should be :
rho = 0.017
l = 100 km = 100.000 m
A = 0.8 cm2 = 0.008 dm2 = 0.00008 m2
R = rho * l/A
R = 0.017 * (100.000/0.00008) = 21250000 ohm
This is totally different from the formula U/I = R !!!!!
I'll give a an example, try to solve this one :
What is R (using R = rho * l/A ) when
A = 10 dm2
l = 30 m
rho = 0.5
R =????
Solve R
With the R you calculated here
you go on with this question (using U/I=R is equal (if rewritten) to R*I =U ) :
U = ?????
I = 5000 mA
R = what you calculated in the first question.
I'll check in later this day, if you still can't solve it email me.
Hope this helps
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[This message has been edited by Mirac Honorguard (edited 10-22-2001).]