A solenoid with an iron core and a bulb in series are connected to a d.c. source. When the iron core is removed from the solenoid, the brightness of the bulb will

remain unaffected

The correct answer is Option (3) → remain unaffected

• In a D.C. circuit, after the initial switching moment, the current becomes constant.
• Inductance only matters when there is a change in current. Once steady state is reached, the inductor behaves like an ordinary conductor (no inductive opposition).
• Although the iron core changes the inductance, it does not affect resistance, and hence does not affect steady current.
• Therefore, removing the iron core does not change the current, so the brightness of the bulb remains the same.