bulb is connected in a closed surface containing air cored solenoid and the battery. how does the brightness of the bulbs changed when
1)number of turn in the coil is increased
2)an iron rod is introduced in the coil
In both the cases the brighteness of bulb is reduced because of the increase in inductance of the coil. Therefore must of the potential difference appears across the coil only. And the bulb gets dimmer.
Hope it helps!
Hope it helps!