A solenoid is con

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This problem is based on Lenz’s law and according to this law, the direction of induced emf or current in a circuit is such as to oppose the cause that produces it. The current will decrease. This is because on inserting an iron core in the solenoid, magnetic field and hence magnetic flux linked with the solenoid increases. As per Lenz's law, the emf induced in the solenoid will oppose this increase, which can be achieved by a decrease in current.