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
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → remain unaffected
With a steady d.c. current, \( dI/dt = 0 \), so the solenoid has no induced emf and no reactance. It behaves only as its resistance, and the current is fixed by the resistances of the circuit.
\( \displaystyle I = \frac{V}{R_{\mathrm{bulb}} + R_{\mathrm{coil}}} \)
Removing the iron core lowers the inductance of the solenoid but does not change any resistance. So the steady current, and the brightness of the bulb, remain the same.