A parallel-plate capacitor is made of two square plates 25 cm on a side and 0.5 mm apart. The capacitor is
connected to a 60-V battery.
Hint
a. What is the energy stored in the capacitor?
Energy stored in the capacitor is
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b. With the battery still connected, the plates are pulled apart to a separation of 1 mm. What is the
energy stored in the capacitor now?
Energy now stored in the capacitor is
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c. This time, starting from situation in (a), with the batteries disconnected (but capacitors still
charged), the plates are pulled apart to a separation of 1 mm. What is the energy stored in the
capacitor now?
Energy now stored in the capacitor is
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d. Comparing your results in (b) and (c) above, it makes sense that the energy stored in the capacitor
increases in (c), because the work done in separating the plates is stored as the electrostatic
potential energy.
In (b), why does the energy decrease even though work is done in separating the plates?
The energy due to work done goes into the battery.
A negative work is done in separating the plates.
The energy is not conserved in static electricity.
The energy stored in the capacitor does not include work done on the charges.
