JEE Mains Model Paper 12

As the iron rod is inserted, the magnetic field inside the coil magnetises the iron increasingthe magnetic field inside it. Hence, the inductance of the coil increases. Consequently, theinductive reactance of the coil increases. As a result, a larger fraction of the applied ACvoltage appears across the inductor, leaving less voltage across the bulb. Therefore, the glowof the light bulb decreases.