Easy MCQ +4 / -1 PYQ · JEE Mains 2021

In a series LCR resonance circuit, if we change the resistance only, from a lower to higher value :

  1. A The bandwidth of resonance circuit will increase. Correct answer
  2. B The resonance frequency will increase.
  3. C The quality factor will increase.
  4. D The quality factor and the resonance frequency will remain constant.

Solution

${\omega } = {1 \over {\sqrt {LC} }}$ <br><br>$\Rightarrow$ 2$\pi$f = ${1 \over {\sqrt {LC} }}$ <br><br>$\Rightarrow$ f = ${1 \over {2\pi \sqrt {LC} }}$ <br><br>f does not depends on resistance(R). <br><br>Quality factor, $Q = {{\omega L} \over R}$ <br><br>$\Rightarrow$ $Q \propto {1 \over R}$ <br><br>So if R increase then Q will decrease. <br><br>Also, $Q = {{\omega L} \over R} = {\omega \over {\Delta \beta}}$ <br><br>where $\Delta \beta$ = bandwidth <br><br>$\Delta \beta = {R \over L}$ <br><br>So if R increase then $\Delta \beta$ will increase too.

About this question

Subject: Physics · Chapter: Alternating Current · Topic: AC Circuits: R, L, C

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