a. \(R=p\dfrac{l}{S}=2,8.10^{-8}\dfrac{1000}{0,5.10^{-6}}=5600\left(\Omega\right)\)
b. \(I=\dfrac{U}{R}=\dfrac{28}{5600}=5.10^{-3}\left(A\right)\)
c. \(C=\pi d=3,14.0,08=0,2512\left(m\right)\)
\(\Rightarrow N=\dfrac{l}{C}=\dfrac{1000}{0,2512}\simeq3980,9\left(vong\right)\)