Practice question · Multiple choice
A capacitor stays connected to a battery while its plates are pulled apart. What happens to the stored energy?
Hints
- At fixed voltage, which form of the energy expression has a constant in it?
- U = half C V squared, and C falls as the plates separate.
Show the answer
B. It falls, because charge flows back into the battery
Why
At fixed the right form is , and falls, so the energy decreases: charge returns to the battery. The same mechanical action raises the energy at fixed charge and lowers it at fixed voltage, which is why naming the constraint matters.
Practise Electrostatic Energy and Forces
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