Engineering Resistance of a wire around the Earth

AI Thread Summary
The discussion revolves around calculating the change in resistance of a wire encircling the Earth when its radius increases by one meter. The initial resistance is calculated using the formula R₀ = ρ(l/A), and the change in length due to the radius increase is determined as ΔL = 2π(r_E + 1) - l. The final change in resistance is found to be ΔR = 3.4 x 10⁻⁴ Ω. Participants express skepticism about the simplicity of the result, but confirm that the math is correct, noting that adding approximately 6.28 meters of wire is indeed sufficient to raise the wire by one meter around the Earth. The conversation emphasizes the importance of trusting one's calculations while also validating them.
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Homework Statement
Homework statement in the image.
Relevant Equations
$$R=\rho\frac{l}{A}$$
$$l=2\pi r$$
Hey! I had a question about this problem.

I did (1) Using
$$R_{0}=\rho\frac{l}{A}$$

For (2) I assume the question means that the radius increases by a meter.
So I used $$\bigtriangleup L = 2\pi (r_{E}+1) - l$$
and then I used that L to find the new R. Then I said $$\bigtriangleup R = R-R_{0}$$

Does that seem right? This seems too simple to be right.

My final answer was:
$$\bigtriangleup R = 3.4 \cdot 10^{-4} \Omega$$
 

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'Too simple' is not an argument ...
What could possible be wrong ?

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BvU said:
'Too simple' is not an argument ...
What could possible be wrong ?

##\ ##
I don’t see anything wrong with my steps. I think they are all logically sound. It’s more so that I’m paranoid and don’t want to lose points on homework for no reason really.
 
PF isn't in the business of stamp-approving homework. It wouldn't help anyone. You do your calculation, get a result and check it. Twice if you want, three times if you are paranoid :smile:

Have some faith in your work ... :wink:

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I find it pretty hard to believe that adding a mere 6.28 m of wire is enough to lift it by 1 meter off the ground all the way around the Earth, but it does indeed.
 
vela said:
I find it pretty hard to believe that adding a mere 6.28 m of wire is enough to lift it by 1 meter off the ground all the way around the Earth, but it does indeed.
It seemed unbelievable when I first heard this one, but the math bears it out.
##C = 2\pi r \Rightarrow \Delta C = 2\pi \Delta r## -- this is an equality due to the linearity of this function.
If ##\Delta r = 1 \text{ meter}##, then ##\Delta C = 2\pi \cdot 1 \approx 6.28 \text{ meters}##
 
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