A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when

Options

(a) number of turns in the coil is reduced
(b) a capacitance of reactance Xc = Xl is included in the same circuit
(c) an iron rod is inserted in the coil
(d) frequency of the AC source is decreased

Correct Answer:

an iron rod is inserted in the coil

Explanation:

By inserting iron rod in the coil, L ↑ z ↑ I ↓ so brightness ↓