As the flux is produced in response to the current, the flux induced by a current is proportional to the current Thus, change in flux induces a current and a voltage which is proportional to the rate of change of flux. This is similar to Ohm's Law (V = IR). Thus we can say ΦB ∝ IAs we know  ΦB=B⋅A   Where B = µ0NI[µ0 (permeability constant) = 4π10-7 T ]Therefore, ΦB = µ0NIA