Two identical parallel-plate capacitors are connected in series to a 100 V battery. A dielectric of K=4 is inserted into the second capacitor. The final voltages across the first and second capacitors are:
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Question

Two identical parallel-plate capacitors are connected in series to a 100 V battery. A dielectric of K=4 is inserted into the second capacitor. The final voltages across the first and second capacitors are:

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G1 Physics · Accepted Answer

After insertion the capacitances are C and 4C in series, carrying equal charge. Voltages divide inversely with capacitance: V₁:V₂=4:1 and V₁+V₂=100 V. Therefore V₁=80 V and V₂=20 V. Correct answer: B.