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Three capacitors having capacitances of 8.4, 8.4, and 4.2
Chapter 24, Problem 61P(choose chapter or problem)
Three capacitors having capacitances of 8.4, 8.4, and 4.2 µF are connected in series across a 36-V potential difference. (a) What is the charge on the 4.2-µF capacitor? (b) What is the total energy stored in all three capacitors? (c) The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other, with the positively charged plates connected together. What is the voltage across each capacitor in the parallel combination? (d) What is the total energy now stored in the capacitors?
Questions & Answers
QUESTION:
Three capacitors having capacitances of 8.4, 8.4, and 4.2 µF are connected in series across a 36-V potential difference. (a) What is the charge on the 4.2-µF capacitor? (b) What is the total energy stored in all three capacitors? (c) The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other, with the positively charged plates connected together. What is the voltage across each capacitor in the parallel combination? (d) What is the total energy now stored in the capacitors?
ANSWER:Introduction First we have to calculate the charge stored in the 4.2 µC capacitor when the given three resistance are connected parallely. Then we have to calculate the total energy stored in the combination of the capacitors. Finally we have to calculate voltage difference across the capacitors and the total energy stored in the capacitor if the capacitors are now connected parallely. Step 1 If the capacitors are connected in series, the charge stored in each capacitor will be same. The equivalent capacitor of the combination is So we have Hence the charge of the capacitor is Hence the charge at the 4.2 µF capacitor will also be 75.6 µC.