Current/Voltage/Resistance HELP

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SUMMARY

The discussion centers on calculating the current flowing through a hollow nichrome tube connected to a 3.0V battery. The user initially applied the formula I = V/R, using R = (ρ*L)/A, where L is the length, A is the cross-sectional area, and ρ is the resistivity of nichrome. The user incorrectly calculated the area by using diameters instead of radii, leading to an erroneous resistance value and an incorrect current calculation of 36.44A instead of the correct 9.1A.

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krugertown
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a 20cm long hollow nichrome tube of inner diameter 2.8mm, outer diameter 3.0mm is connected to a 3.0V battery. What is the current in the tube?



I think this is a I = V/R problem. So i used R=([tex]\rho[/tex]*L)/A. Where L is the length of the wire and A is the outer area minus the inner area and rho is the resistivity of nichrome.


A =.003^2*[tex]\pi[/tex] - .0028^2*[tex]\pi[/tex] = 3.64*10^-6
R = ((1.5*10^-6) * (.02))/3.64*10^-6 = .0823
I = 3/.0823 = 36.44Amps

However the answer is 9.1A apparently. Where have i gone wrong?

Thanks!

btw if the greek symbols appear superscript they are not supposed to be I can't quite figure that part out
 
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You made a simple error, 3.0mm and 2.8mm are diameters, not radii.

Area is [tex]\pi r^2[/tex]
 
haha thanks! spent 45 minutes on that problem!
 

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