Question

An inductor L of incluctance X_L is connected in series with a bulb B and an a.c. source. How would brightness of the bulb change when (i) number of turn in the inductor is reduced, (ii) an iron rod is inserted in the inductor and (iii) a capacitor of reactance X_C = X_L is inserted in series in the circuit. Justify your answer in each case.

Answer 1

(i) Increases :

X_L = ωL

As number of turns decreases, L decreases, hence current through bulb increases / voltage across bulb increases.

(ii) Decreases :

Iron rod increases the inductance, which increases X_L, hence current through the bulb decreases / voltage across bulb decreases.

(iii) Increases :

Under this condition (X_C = X_L) the current through the bulb will become maximum / increase.