1. The problem statement, all variables and given/known data 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? 3. 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.