Question

A long straight solenoid has n turns per unit length. An alternating current I = I_m sin ωt flows through it. Find the displacement current density as a function of the distance r from the solenoid axis. The cross-sectional radius of the solenoid equals R.

Answer 1

Inside the solenoid, there is a magnetic field, 

Since this varies in time there is an associated electric field. This is obtained by using,

The associated displacement current density is,

The answer, given in the book, is dimensionally incorrect without the factor ε₀.