Consider the combination of 2 capacitors C1 and C2 with C2 > C1, when connected in parallel, the equivalent capacitance is ${{15} \over 4}$ times the equivalent capacitance of the same connected in series. Calculate the ratio of capacitors, ${{{C_2}} \over {{C_1}}}$.
Solution
When connected in parallel<br><br>C<sub>eq</sub> = C<sub>1</sub> + C<sub>2</sub><br><br>When in series<br><br>$C{'_{eq}} = {{{C_1}{C_2}} \over {{C_1} + {C_2}}}$<br><br>$${C_1} + {C_2} = {{15} \over 4}\left( {{{{C_1}{C_2}} \over {{C_1} + {C_2}}}} \right)$$<br><br>$4{({C_1} + {C_2})^2} = 15{C_1}{C_2}$<br><br>$4{C_1}^2 + 4{C_2}^2 - 7{C_1}{C_2} = 0$<br><br>dividing by ${C_1}^2$<br><br>$4{\left( {{{{C_2}} \over {{C_1}}}} \right)^2} - {{7{C_2}} \over {{C_1}}} + 4 = 0$<br><br>Let ${{{C_2}} \over {{C_1}}} = x$<br><br>$4{x^2} - 7x + 4 = 0$<br><br>${b^2} - 4ac = 49 - 64 < 0$<br><br>$\therefore$ No solution exixts.
About this question
Subject: Physics · Chapter: Electrostatics · Topic: Coulomb's Law
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