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Question: Answered & Verified by Expert
A coil of self-inductance $L$ is connected in series with a bulb $B$ and an $A C$ source. Brightness of the bulb decreases when
PhysicsAlternating CurrentJEE Main
Options:
  • A frequency of the $\mathrm{AC}$ 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
Solution:
2259 Upvotes Verified Answer
The correct answer is: an iron rod is inserted in the coil
As $Z=\sqrt{R^2+X_L^2}=\sqrt{R^2+(2 \pi f V L)^2}$
As $/=\frac{V}{Z}, P=/^2 R$
i.e., $V \uparrow, L \uparrow \Rightarrow Z \uparrow, / \downarrow$ and $P \downarrow$

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