Refer to Prob. 7.16, to which the correct answer was
E(s,t)=2πμ0I0ωsin(ωt)ln(sa)z^.
(a) Find the displacement current density Jd.
(b) Integrate it to get the total displacement current,
Id=∫Jd⋅da.
(c) Compare Id and I. (What's their ratio?) If the outer cylinder were, say, 2 mm in diameter, how high would the frequency have to be, for Id to be 1\% of I? [This problem is designed to indicate why Faraday never discovered displacement currents, and why it is ordinarily safe to ignore them unless the frequency is extremely high.]