A commercial capacitor is to be constructed as shown in the figure below. This p

Question

A commercial capacitor is to be constructed as shown in the figure below. This particular capacitor is made from two strips of aluminum foil separated by a strip of paraffin-coated paper. Each strip of foil and paper is 7.60 cm wide. The foil is 0.003 50 mm thick, and the paper is 0.030 0 mm thick and has a dielectric constant of 3.70. What length should the strips have if a capacitance of 9.50 times 10-8 F is desired before the capacitor is rolled up? (Adding a second strip of paper and rolling the capacitor would effectively double its capacitance by allowing charge storage on both sides of each strip of foil.)

Explanation / Answer

You need to know the formula to calculate the capacitance of a parallel plate capacitor:

Capacitance = Permittivity x Area / thickness (Where permittivity = permittivity of free space x dielectric constant)

Rearrange the formula so that you can calculate the area of the plates.
Divide the area by the width to get the length required.

The thickness you need in the equation is the thickness of the paper, the thickness of the plates makes no difference.

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