A capacitor is made from two hollow, coaxial, iron cylinders, one inside the oth

Question

A capacitor is made from two hollow, coaxial, iron cylinders, one inside the other. The inner cylinder is negatively charged and the outer is positively charged; the magnitude of the charge on each is 15.5pC . The inner cylinder has a radius of 0.500mm , the outer one has a radius of 6.80mm , and the length of each cylinder is 23.0cm

A) What is the capacitance? Use 8.85*10^-12

B) What applied potential difference is necessary to produce these charges on the cylinders?

Answer both for the points!

Explanation / Answer

The capacitance of a cylindrical capacitor is

C =   2 pi L epsilon / ln(b/a)

b and a are the outer and inner radii.

C = 2 pi * 0.23 * 8.85 x10-12 / ln(6.8/0.5)

= 4.90 x 10-12 F = 4.9 pF

--------------------------------------------

V = Q / C

= 15.5 pC / 4.9 pF

= 3.16 V

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