Posted by **Spencer** on Tuesday, February 12, 2008 at 11:50am.

A 68.0 g hollow copper cylinder is 90.0 cm long and has an inner diameter of 1.0 cm. The current density along the length of the cylinder is 1.60×10^5(A/m^2). What is the current in the cylinder? Ive tried many ways but am not getting the correct answer.

- Physics E&M -
**bobpursley**, Tuesday, February 12, 2008 at 12:01pm
You have to measure the area of the cylinder, that is, the outer radius area minus the inner radius.

You are given the mass, you can look up the density.

mass=density*PI(radiusouter^2-radiusinner^2)*length

Now, solve for (radiusouter^2-radiuinner^2)

Areacopper= PI (radiusouter^2-radiusinner^2) or

areacopper= masscopper/(density*lenght)

current= currentdensity*area

So, did the size of the cylinder affect anything?

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