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 12.0 pC. The inner cylinder has a radius of 0.250 mm, the outer one has a radius of 5.00 mm, and the length of each cylinder is 22.0 cm.1.What is the capacitance? Use 8.854×10−12 F/m for the permittivity of free space.2.What applied potential difference is necessary to produce these charges on the cylinders?

Answer 1

Answer: 1) 17.65 * 10^-12 C/V; 2) 0.68 V

Explanation: In order to calculate the capacitance of one cylinder capacitor we have to use the following expression:

$C=\frac{2\pi \epsilon o L}{ln (b/a)}$ where and b are the inner and outer radius of teh cylinder, respectively. L is length of the cylinder.

Finally we also kwn that C=Q/ΔV

then we have

ΔV =Q/C

ΔV = 12 * 10^-12/17.65*10^-12= 0.68V