A coil of self inductance L is connected in series with a bulb B and an a.c. source. Brightness of the bulb decreases when (a) frequency of a.c. source is decreased. (b) number of turns in the coil is reduced. (c) a capacitance of reactance (XL - XC) is included in the same circuit. (d) an iron rod is inserted in the coil.

Answer: (d). Iron rod raises L, so XL = ω L increases and current I = (V)/(√(R²+XL²)) falls. Lower frequency, fewer turns, or a series capacitor (cancelling XL) all reduce net reactance and brighten the bulb. So the answer is (d) an iron rod is inserted in the coil.

A coil of self inductance L is connected in series with a bulb B and… | MHT CET 2024 (4 May, Shift 2)

Q22MHT CET 2024 · 4 MAY · SHIFT 2Easy

RL and RC Series Circuits

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

Show answer and solution

Answer: (d)

Iron rod raises $L$ , so $X_L = \omega L$ increases and current $I = \frac{V}{\sqrt{R^2+X_L^2}}$ falls.
Lower frequency, fewer turns, or a series capacitor (cancelling $X_L$ ) all reduce net reactance and brighten the bulb.
So the answer is (d) an iron rod is inserted in the coil.

Report a mistake

RL and RC Series Circuits question from MHT CET 2024 (4 May, Shift 2)

More questions on RL and RC Series Circuits