A solenoid 30 cm long is made by winding 2000 turns of wire on an iron rod whose cross-sectional area is 1.5 cm². If the relative permeability of the iron is 600, what is the self-inductance of the solenoid? What average emf is induced in the solenoid as the current in it is decreased from 0.60 A to 0.10 A in a time of 0.030 s? Refer back to Problem 34.2.

Problem 34.2

A long air-core solenoid has cross-sectional area A and N loops of wire on its length d. 

(a) Find its self-inductance. 

(b) What is its inductance if the core material has a permeability of μ?