Question

What happens if iron rod is inserted in inductor connected to lamp and AC source in series

Answer 1

As the iron rod is inserted, the magnetic field inside the coil magnetizes the iron increasing the magnetic field inside it. Hence, the inductance of the coil increases. Consequently, the inductive reactance of the coil increases. As a result, a larger fraction of the applied ac voltage appears across the inductor, leaving less voltage across the bulb. Therefore, the glow of the light bulb decreases.
In case of dc source the brightness of the bulb remains unchanged as the reactance offered by a coil to a d.c. current is zero.
Reduced;A bulb connected to the coil with the more number of turns lights up brighter while the bulb that is connected to the coil with fewer number of turns is dimmer.