A bulb B and an inductor L are connected in series to an ac source as shown in the figure.
The switch is closed and after some time an iron rod is inserted into the core of inductor. The brightness of bulb
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → will decrease
In an ac circuit the inductor opposes the current through its inductive reactance \( X_L = \omega L \). Inserting an iron rod into the core greatly increases the inductance because iron has a large relative permeability.
\( \displaystyle Z = \sqrt{R^{2} + (\omega L)^{2}} \)
\( \displaystyle I_{\mathrm{rms}} = \frac{V_{\mathrm{rms}}}{Z} \)
As L increases, Z increases and the current decreases. The power in the bulb, \( I_{\mathrm{rms}}^{2}R \), falls, so the bulb becomes dimmer.
NCERT (2026-27):
AC Voltage Applied to a Capacitor – …
