Charge Sharing
Charge Sharing
- Connected capacitors reach the same final p.d. Total charge is conserved, but stored energy is not.
Use equal p.d. and conserved charge
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Worked example
C shares charge with 3C
Why stored energy decreases
Charge moves through the connecting wires. Some electric potential energy becomes thermal energy and other energy in the brief current pulse.
Worked example
A recent charge-sharing result
A 470 μF capacitor initially stores 19 mJ and is connected to an uncharged 180 μF capacitor (9702/41/O/N/25 Q6(b)(iii)).
Answer
Common mistake
Conserve total charge during sharing. Do not set initial stored energy equal to final stored energy.
Your turnquick check
After charge sharing, is the final stored energy equal to, greater than or less than the initial stored energy? State where the missing energy goes.
Show worked answer
Answer: It is less than the initial stored energy.
Energy is transferred mainly to thermal energy in the connecting circuit and surroundings.