In the shown RC circuit, total energy 3.6×10⁻³ J is dissipated in the 10 Ω resistor after switch S is closed. The capacitor is 2 μF. Find its initial charge.
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Question

In the shown RC circuit, total energy 3.6×10⁻³ J is dissipated in the 10 Ω resistor after switch S is closed. The capacitor is 2 μF. Find its initial charge.

G1 Physics · Accepted Answer

All initial capacitor energy is dissipated as heat: Q²/(2C)=3.6×10⁻³. Thus Q=√(2CU)=√[2×2×10⁻⁶×3.6×10⁻³]=120×10⁻⁶ C=120 μC. Correct answer: B.