A light bulb and an open coil inductor are connected to an ac source through a key as shown in Fig. The switch is closed and after sometime, an iron rod is inserted inot the interior of the inductor. The glow of the ligth bulb (a) increases (b) decreases (c) is unchanged as the iron is inserted. Give your answer with reasosns. What will be your answer if ac source is replaced by dc source ?

Explanation

When an iron rod is inserted into the interior of the inductor, inductance (L) of the coil increases, increasing thereby the inductive reactance `X_(L) = omega L`. The current `I_(v) = E_(v)//X_(L)` decreases. Therefore, glow of light bulb decreases.
If ac source is replaced by dc source of same voltage , glow of light of the bulb is much more (`:' X_(L) = omega L = 2 pi v L = 0)`. However, this glow does not change on inserting iron rod.