A bulb and an iron core inductor are connected to an AC source through key as shown in figure: 

The bulb glows with certain brightness. Now iron rod is taken out of the inductor. Then the brightness of bulb: 

increases 

$ \text{If iron rod is removed then the inductance will decrease}$

$ \Rightarrow X_L = \omega L \text{will decrease , i.e Z will decrease}$

$\Rightarrow \text{ Current will increase i.e the brightness of bulb will increase}$