Charge Volume Density To Charge Per Unit Length

  • #1

Homework Statement

I took a screen shot so I did not leave anything out.

Homework Equations

Surface area, and volume of a sphere.

The Attempt at a Solution

I am trying to find the linear charge density from the charge volume density. I got it explained from a friend. It was right, but made no sense. He did it by taking the volume density, and multiplying it by the charge volume density by pi, and (outer r2 - inner r2).

So he did -657 * pi * (.0422 - .0262)

Can someone explain to me how this is right?
  • #2
It's the total charge per unit length due to the outer insulator. Charge = voume charge density x volume. The volume of the insulator is pi(r2^2 - r1^2) x 1 unit length. Multiply by the charge density rho and you have your answer.

Of course, the complete answer must include the linear charge density of the wire as well.
  • #3
Calculate the total charge Q of a length ##l## of the insulator. Then divide Q by ##l##.

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