A parallel plate capacitor whose capacitance C is 14 pF is charged by a battery to a potential difference V = 12 V between its plates. The charging battery is now disconnected and a porcelin plate with k = 7 is inserted between the plates, then the plate would oscillate back and forth between the plates with a constant mechanical energy of _____________ pJ. (Assume no friction)
Answer (integer)
864
Solution
${U_i} = {1 \over 2}c{v^2}$<br><br>$= {1 \over 2} \times 14 \times {(12)^2}$ pJ<br><br>= 1008 pJ<br><br>${U_f} = {{{Q^2}} \over {2kC}}$<br><br>$= {{{{(14 \times 12)}^2}} \over {2 \times 7 \times 14}}$<br><br>= 144 pJ<br><br>oscillating energy = U<sub>i</sub> $-$ U<sub>f</sub><br><br>= 1008 $-$ 144<br><br>= 864 pJ
About this question
Subject: Physics · Chapter: Electrostatics · Topic: Electric Potential and Capacitance
This question is part of PrepWiser's free JEE Main question bank. 132 more solved questions on Electrostatics are available — start with the harder ones if your accuracy is >70%.