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

Capacitance is given by

C = k*e0*A/d

A = L*w

w = 3.00 cm = 0.03 m

L = ?

e0 = 8.85*10^-12

d = 0.025*10^-3 m

k = 3.7

C = 7*10^-8 F

C = k*e0*L*w/d

L = 7*10^-8*0.025*10^-3/(3.7*8.85*10^-12*0.03)

L = 1.78 m

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