The switch in the circuit shown in the figure below is closed, and the lightbulb glows steadily. The inductor is a simple air-core solenoid. An iron rod is inserted into the interior of the solenoid, increasing the magnitude of the magnetic field in the solenoid. As the rod is inserted, the brightness of the lightbulb

Question

A) Increases

B)Decreases

C)Stays the same

I know its decreased, by why?

This is my thought process, decrease because the current will decrease in order to counteract the increase in magnetic field.
A current will be induced to resist the change in the magnetic field. That current will try to reduce the magnetic field within the solenoid. Use the right hand rule to figure out which way the current will be induced. If it aligns with the source, the bulb becomes brighter. If it opposes the source, the bulb will become dimmer.