CBSE Class 12 · 2004 · Electromagnetic InductionVery Short Answer

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A solenoid with an iron core and a bulb are connected to a d.c. source. How does the brightness of the bulb change when the iron core is removed from the solenoid?

Answer: No change in brightness.

Solution

With a steady d.c. source the current finally settles to

I = V / R

, where

R

is the resistance of the circuit; this value does not depend on the self-inductance.
The iron core only alters

L

, which affects the circuit during the brief build-up of current, not the final steady current.
Therefore removing the core leaves the steady current unchanged and

the brightness of the bulb stays the same

CBSE Class 12 Board · 2004 · Subjective

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