- #1
vorcil
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Homework Statement
A sheet of copper 0.6m in total length and 0.2m wide is folded to create a uniform spacing of 1mm.
the sheet is 1mm thick. a potential difference of 1mV is applied at the open end in such a way that the current is distrubuted unformly over the cross sectional area of the metal.
I can neglect the effects of the fold (the vertical bit)
http://yfrog.com/f/5mpicbvwp/
(i also forgot to draw in the battery, connecting the two ends of the open side, it has a potential difference of 1mV)
Find the resistance of the sheet,
and the current.
Homework Equations
https://secure.wikimedia.org/wikipedia/en/wiki/Sheet_resistance
In griffiths, I do not see this formula anywhere, however I'm going to use it anyway.
properties of copper:
electrical resistivity: 1.7*10^-8 ohms per metre
density: 8.9*10^3 kg m^-3
atomic weight = 64amu
The Attempt at a Solution
[tex] R = \rho \frac{L}{A} \Rightarrow A = 0.2m * 1mm [/tex]
the length of the sheet is 0.6m
plugging in the values
[tex] R = (1.7*10^-8) * \frac{0.6}{0.2(1*10^-3)} = (5.1*10^-5) =51micro ohms [/tex]
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finding the current through the sheet, I'm just going to use Ohm's law,
[tex] \mathbf{J} = \sigma\mathbf{E} \Rightarrow \mathbf{V=IR} [/tex]
plugging in the values, 1mV and 51 micro ohms, I get 19.6 Amps,
however I don't know if I'm right, because that seems superlarge to me?
where have I gone wrong?
-> can I not use the formula on this page? https://secure.wikimedia.org/wikipedia/en/wiki/Sheet_resistance