Verified Solution • 2025–26 Session moderate

QJEEM19Ph8c63: JEE Main 2019 Physics - Class 12 JEEM19Ph8c63 Solution: A capacitor with capacitance 5μF is charged to 5μC. If the…

A capacitor with capacitance 5μF is charged to 5μC. If the plates are pulled apart to reduce the capacitance to 2μF, how much work is done ?

Multiple Choice Options

  • A 2.16 × 10–6 J
  • B 2.55 × 10–6 J
  • C 3.75 × 10–6 J
  • D 6.25 × 10–6 J

Step-by-Step Verified Solution

Work done = Δ\Delta U

= Uf – Ui

=q22Cr−q22Ci= {{{q^2}} \over {2{C_r}}} - {{{q^2}} \over {2{C_i}}}

=(5×10−6)22.(12×10−6−15×10−6)= {{{{\left( {5 \times {{10}^{ - 6}}} \right)}^2}} \over 2}.\left( {{1 \over {2 \times {{10}^{ - 6}}}} - {1 \over {5 \times {{10}^{ - 6}}}}} \right)

=154×10−6=3.75×10−6J= {{15} \over 4} \times {10^{ - 6}} = 3.75{\rm{ }} \times {\rm{ }}{10^{-6}}{\rm{ }}J

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