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- Homework Statement
- A copper wire has an internal diameter ##d_1## of ##10## ##cm## and an external diameter ##d_2## of 20 ##cm##. If the wire is ##20m## long what is the resistance of the wire?

- Homework Equations
- ##R=\rho\frac{l}{\Sigma}##

What i did is: ##R=\rho\frac{l}{\Sigma}=\rho\frac{l}{d_2^2\pi-d_1^2\pi}##

The problem is that I don't have ##\rho##. Is there a way to find ##R## without knowing it?

Many thanks.

The problem is that I don't have ##\rho##. Is there a way to find ##R## without knowing it?

Many thanks.