A coil and a bulb are connected in series. A soft iron core is inserted into the coil. What will be the effect on the intensity of the bulb if-1. The setup is connected to a D.C. source. 2. The setup is connected to an A.C. source.

As iron rod is nserted, 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.

glow of the bulb increases.

In case of DC source, brightness remains unchanged. As the reactance offered by a coil to D.C. current is zero

when coil and bulb are connected to AC source,insertion of an iron rod causes an induced current in the coil due to the change in magnetic flux linked by the coil.According to Lenzs law the direction of induced current will be in such a way that it opposes the cause that produced it.Hence its direction is opposite to actual current,over all current in the circuit decreases and brightness also decrease..