
#1
Sep2613, 09:54 PM

P: 599

1. The problem statement, all variables and given/known data
The current density in a cylindrical conductor of radius a placed along the zaxis is J=10e^(1ρ/a)Uz Find the current through the crosssection of the conductor. 2. Relevant equations I=JA A=(pi)a^2 3. The attempt at a solution So far I have this I=10e^(1ρ/a)Uz((pi)a^2) which I assume I am to integrate but what should I integrate with respect too and what should the limits be I am guessing from 0 to a? 



#2
Sep2713, 02:35 AM

Thanks
P: 1,316

You integrate the flow normal to the cross section through which it is flowing.




#3
Sep2713, 09:55 AM

P: 599

So that would be along the x or y?




#4
Sep2713, 09:55 AM

P: 599

Current through the conductor
The normal is the perpendicular vector right?




#5
Sep2713, 11:46 AM

Thanks
P: 1,316

Yes, the normal is perpendicular to the surface.




#6
Sep2713, 03:28 PM

P: 599

ok so a normal vector equals to Uz/Uz (where the bottom Uz is the length of Uz it is in between those two absolute value mark things). Do you have any more hints on how to set this up




#7
Sep2813, 02:50 AM

Thanks
P: 1,316

Your problem states that the current is flowing along the axis Uz, hence it is perpendicular to the cross section formed by the xy plane.
So you just have to integrate the density given as it crosses the circle of radius a defined by the cylinder of the wire. Since the axis passes along the center of the wire it would be easiest to switch to cylindrical coordinates for this integration. 



#8
Sep2813, 02:56 PM

P: 599

∫JdS=Ienc where dS=ρd(phi)dρ in cylindrical right?



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