Question

A solenoid is connected to a battery so that a steady current flow through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain.

Answer 1

Lenz’s law: An induced electromotive force $\left(emf\right)$ always gives rise to a current whose magnetic field opposes the change in original magnetic flux.
As the iron core is inserted in the solenoid, the magnetic field increases due to magnetization of iron core and the flux increases. Lenz’s law implies that induced $e.m.f$. should resist the increase in magnetic flux, which can be achieved by a decrease in current.

Therefore, by inserting of iron core into the solenoid, current will decrease.