NEET Physics Alternating Current / प्रत्यावर्ती धारा NEET PYQ-Alternating Current

A coil of self-inductance L is connected in series with a bulb - B and an AC source. Brightness of the bulb decreases when [NEET 2013]

A) frequency of the AC source is decreased

B) number of turns in the coil is reduced

C) a capacitance of reactance \[{{X}_{C}}={{X}_{L}}\] is included in the same circuit

D) an iron rod is inserted in the coil

Correct Answer: D

Solution :

As \[Z=\sqrt{{{R}^{2}}+X_{L}^{2}}=\sqrt{{{R}^{2}}+{{(2\pi fvL)}^{2}}}\]

As \[l=\frac{V}{Z},p={{l}^{2}}R\]

i.e., \[V\uparrow ,L\uparrow \Rightarrow Z\uparrow ,l\downarrow \]

and \[P\downarrow \]