Q. A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when -
A) frequency of the AC source is decreased
B) number of turns in the coil is reduced
C) a capacitance of reactance XC = XL is included in the same circuit
D) an iron rod is inserted in the coil
Explanation
[Solution from source] An iron rod increases the inductance L, raising XL = ωL and the impedance, so the current and the bulb's brightness drop. Lowering the frequency, reducing the turns or adding a capacitor with XC = XL all reduce the net reactance and make the bulb brighter. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.