A steel rod, 10 mm diameter and 50 cm long, is formed into a closed nng and uniformly wound with 400 turns of wire A direct current of 0,5 A is passed through the winding and produces a flux density of 0,75 T All the flux links with every turn of the winding 331 Calculate the relative permeability of the steel (4) 332 Calculate the inductance of the coil (3) 333 Calculate the average value of the emf induced when the interruption of the current causes the flux in the steel to decay to 20% cent of its original value in 10 ms