# Currents in a Metal Wire and Shell.?

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A solid conductor with radius 0.8mm is supported by insulating disks on the axis of a conducting cylindrical shell with inner radius 9.1mm and outer radius 9.9mm . The central ...show more

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Current density(J) is the current(I) per area(A).

So J=I/A, however your A is the area of the circle. So we use the equation pi*r^2=A

J=I/pi(r^2)

Its in mm so I will change it just by dividing by a thousand.

1) The inner wire has a radius of 0.8/1000, so J=5.4/(pi*(0.8/1000)^2

2) For the outer shell is J=1.9/(pi*[(9.9/1000)^2-(9.1/1000)^2])

So J=I/A, however your A is the area of the circle. So we use the equation pi*r^2=A

J=I/pi(r^2)

Its in mm so I will change it just by dividing by a thousand.

1) The inner wire has a radius of 0.8/1000, so J=5.4/(pi*(0.8/1000)^2

2) For the outer shell is J=1.9/(pi*[(9.9/1000)^2-(9.1/1000)^2])

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