Question

How far apart would parallel pennies have to be to make a 1.80 pF capacitor? (Estimate the radius of penny to be 1.0 cm.)

Answer 1

Given, capacitance,C= 1.80 pF=1.80×10^-12 F

r=1cm=1×10^-2 m

Therefore,area,A= πr^2=3.14×[10^-2]^2

Area=3.1×10^-4 m^2

Capacitance,C=r0(A/d)

Where, r --- relative static permittivity of dielectric

Relative static permittivity of air~1.00059

0 =8.854×10^-12 F/m (Electric constant)

Ie, distance

d= r​0A/C

d=1.00059×8.854×10^-12×3.1×10^-4/1.8×10^-12

d=1.5 ×10^-3 m= 1.5 mm