JEE Mains · Physics · STD 12 - Electric potential and capacitance
- JEE Mains 2021
- Hard
- MCQ
Consider the combination of \(2\) capacitors \(C _{1}\) and \(C _{2},\) with \(C _{2}> C _{1},\) when connected in parallel, the equivalent capacitance is \(\frac{15}{4}\) time the equivalent capacitance of the same connected in series. Calculate the ratio of capacitors, \(\frac{ C _{2}}{ C _{1}}\)
Pick an option to check your answer.
Answer & Solution
Correct Answer
(D) None of these
Step-by-step Solution
Detailed explanation
When connected in parallel \(C _{ eq }= C _{1}+ C _{2}\)
When in series
\(C _{ eq }^{\prime}=\frac{ C _{1} C _{2}}{ C _{1}+ C _{2}}\)
\(C _{1}+ C _{2}=\frac{15}{4}\left(\frac{ C _{1} C _{2}}{ C _{1}+ C _{2}}\right)\)
\(4\left( C _{1}+ C _{2}\right)^{2}=15 C _{1} C _{2}\)
\(4 C _{1}{ }^{2}+4 C _{2}^{2}-7 C _{1} C _{2}=0\)
dividing by \(C _{1}{ }^{2}\)
\(4\left(\frac{ C _{2}}{ C _{1}}\right)^{2}-\frac{7 C _{2}}{ C _{1}}+4=0\)
Let \(\frac{ C _{2}}{ C _{1}}= x\)
\(4 x^{2}-7 x+4=0\)
\(b ^{2}-4 ac =49-64<0\)
No solution exits981-s782
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