Inserting iron core in an inductor coil

[utkarshakash]

Homework Statement

A coil is connected in series with a bulb and this combination is connected to a DC source. When an iron core is inserted in the coil, what will happen to the brightness of the bulb?

The Attempt at a Solution

When the iron core is inserted, the magnetic field changes. Thus the self inductance also changes. So the brightness of the bulb should change. I don't know if I am correct here.

 

[donpacino]

While it is true that the inductance will change when the core is inserted, there is only a magnetic field when the current through the inductor changes.
A DC source is a source that has a constant voltage.
Therefore the current through the inductor does not change, it remains constant.
Therefore there is no change to the brightness of the bulb.