CBSE Class 12 Physics 2015 Delhi Set 1 Paper

Question : 22

Total: 26

An inductor L of inductance XL is connected in series with a bulb B and an ac source.
How would brightness of the bulb change when (i) number of turn in the inductor is reduced, (ii) an iron rod is inserted in the inductor and (iii) a capacitor of reactance XC=XL is inserted in series in the circuit. Justify your answer in eachcase.

Solution:

Change in the Brightness of the bulb in cases (i), (ii) & (iii) Justification
(i) Increases
XL=ωL As number of turns decreases, L decreases, hence current through bulb increases. / Voltage across bulb increases.
(ii) Decreases
Iron rod increases the inductance which increases XL , hence current through the bulb decreases./ Voltage across bulb decreases.
(iii) Increases
Under this condition (XC=XL) the current through the bulb will become maximum / increase.

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