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Question:

Physics and Resistivity?

A hollow aluminum cylinder is 2.50 m long and has an inner radius of 3.20 cm and an outer radius of 4.60 cm Treat each surface (inner, outer, and the two end faces) as an equipotential surfaceAt room temperature, what will an ohmmeter read if it is connected between the inner and outer surfaces?Any suggestions? Don't really know where to start.

Answer:

Open the cylinder so that it becomes a flat sheet of aluminium Thickness t (4.60 - 3.20) 1.40cm 0.014m Area A (2πr) x 2.50m r mean radius (3.90cm 0.039m) Apply the resistivity equation R ρ.t / A to find R Resistivity of Al at room temp.(20C) ρ 2.65^-8 Ωm t replaces the normal length of conductor (L) in equBecause of the shape of this conductor (v.large surface area compared to 'length') it is normally not reliable to use R ρL/A but, because we can assume the whole of a surface is at the same voltage (equipotential) it's OK to apply it.
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