A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain.
The current will decrease. As the iron core inserted in the solenoid, the magnetic field increases and the flux increases. Lenz's law implies that induced emf should resist this increases, which can be achieved by a decreases in current. However this change will be momentarily.