A commercial capacitor is constructed as in Figure 16.25a. This particular capac

Question

A commercial capacitor is constructed as in Figure 16.25a. This particular capacitor is made from a strip of aluminum foil separated by two strips of paraffin-coated paper. Each strip of foil and paper is 3.00 cm wide. The foil is 0.00400 mm thick, and the paper is 0.025 mm thick and has a dielectric constant of 3.7. What length should the strips be if a capacitance of 7.00 10-8 F is desired before the capacitor is rolled up? (Use the parallel-plate formula. Adding a second strip of paper and rolling up the capacitor doubles its capacitance by allowing both surfaces of each strip of foil to store charge.)
m

Explanation / Answer

let,

width of the strip, w=3cm

thickness of foil, tf=0.004mm

thickness of the paper, d=0.025mm

dielectric constant, k=3.7

capacitance, C=7*10^-8 F

lenth of the capacitor is L

use,

C=K*eo*A/d

(7*10^-8)=3.7*(8.854*10^-12)*A/(0.025*10^-3)

==> A=5.342*10^-2 m^2

area of the plate is,

A=5.342*10^-2 m^2

and

area=l*w

5.342*10^-2=l*(3*10^-2)

===> l=1.78 m

length of strip, l=1.78 m

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