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# I have V, and current for different lengths. I can get R with R=V/length. How does cross sectional area relate to the R vs. length graph?

Ok, thank you for your help. I am trying to find the cross sectional area. I think I'm confused about how to find the C.S.A because I wasn't given ρ (rho). The slope of my Resistance vs. Length graph is 8.7. I would have to manipulate --> R = ρℓ / A into A = ρℓ / R . I would have the values of R and ℓ but I would have two unknowns ρ and A.

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- NCSLv 75 months agoFavorite Answer
It is not true that R=V/length.

You can get resistance R = V / I

where I ("eye") is the current (not l ("ell"), the length)

Furthermore, if you plot R vs length, you must hold the cross-sectional area constant in order to get a meaningful graph.

It might be better to explain what your objective is. I suspect that it is to calculate the resistivity ρ of the wire material.

R = ρℓ / A

so, if you plot R (vertical) vs ℓ/A (horizontal) the slope of the line shoud be the resistivity of the conductor.

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- Andrew SmithLv 75 months ago
Although I could give you the answer there is nothing in the question that gives any clues.

If this was an experiment you would be expected to take a number of pieces of wire of the same length but different diameters and discover the result.

If you take the theory you know that Resistance = resistivity ( a constant) * L/A

so that the gradient of the graph of R vs L is R/L = resistivity / A

ie the gradient of your graph is inversely proportional to the cross sectional area A

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