# Capacitor with a conducting core

A 0.380 m long cylindrical capacitor consists of a solid conducting core with a radius of 1.15 mm and an outer hollow conducting tube with an inner radius of 2.05 mm . The two conductors are separated by air and charged to a potential difference of 6.40 V .

Calculate the charge per length for the capacitor.

lambda =_______ C/m.

Calculate the total charge on the capacitor.

Q=_____ C.

Calculate the capacitance.

C=______ F.

Calculate the energy stored in the capacitor when fully charged.

U=_______ J.

Well i figure out a couple of equations to use but i seem to get them wrong! all are wrong! Any Help!
so the equation i used were :

To Find C = 2 pi €o L ln(r2/r1) = 12.22 *10^-12 F = 12.22 pF.
To Find U = (1/2) C V^2 = 250*10^-12 J = 250 pJ.
To Find Q = C V = 78.2*10^-12 C = 78.2 pC
To Find lambda = Q/L = 2.06*10^-10 C/m = 206 pC/m.

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alphysicist
Homework Helper
To Find C = 2 pi €o L ln(r2/r1) = 12.22 *10^-12 F = 12.22 pF.
Hi sonrie,

This is the wrong formula for the cylindrical capacitor. The natural log is in the denominator.

so the formula should read C= 2 pi Eo L/Ln (r2/r1) Is that correct?

alphysicist
Homework Helper
That looks right to me.