Question

A choke coil and a bulb are connected in series to an a.c source. The bulb shines brightly. How does the brightness change when an iron core is inserted in the choke coil?

Answer 1

The brightness of the bulb decreases when an iron core is inserted in the choke coil.

when a iron core is inserted then the inductance of the choke coil (L) increases, consequently the inductive reactance of the choke coil (wL) increases.

This causes the impedance(Z) of the circuit to increase,

we know that current in an ac cicuit is given as,

i = V/Z

since Z increases so current in the circuit decreases which causes the bulb to dim.