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JEE Main 2024 (5 Apr, Shift 1) · Combination of Capacitors

Combination of Capacitors question from JEE Main 2024 (5 Apr, Shift 1)

Q34JEE Main 2024 · 5 APR · SHIFT 1Medium

Combination of Capacitors

Three capacitors of capacitances 25 μF,30 μF25\ \mu\text{F}, 30\ \mu\text{F} and 45 μF45\ \mu\text{F} are connected in parallel to a supply of 100 V100\text{ V}. Energy stored in the above combination is E. When these capacitors are connected in series to the same supply, the stored energy is 9xE\frac{9}{x}E. The value of xx is _________.

Numerical answer type. Work it out, then open the answer.

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Answer: 86

  1. Same supply: U∝CU \propto C, so EsE=CsCp\frac{E_s}{E} = \frac{C_s}{C_p}.
  2. Cp=25+30+45=100 μFC_p = 25 + 30 + 45 = 100\ \mu\text{F}.
  3. 1Cs=125+130+145=18+15+10450=43450⇒Cs=45043 μF\frac{1}{C_s} = \frac{1}{25} + \frac{1}{30} + \frac{1}{45} = \frac{18+15+10}{450} = \frac{43}{450} \Rightarrow C_s = \frac{450}{43}\ \mu\text{F}.
  4. EsE=45043×100=986\frac{E_s}{E} = \frac{450}{43\times100} = \frac{9}{86}, so x=86x = 86.
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