The dielectric in a capacitor is changed to a material with a dielectric constan
ID: 1423970 • Letter: T
Question
The dielectric in a capacitor is changed to a material with a dielectric constant that is larger by a factor of seven. If the charge on the capacitor is held fixed, by what factor does the energy stored in the capacitor change?
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Explain why the energy is different in the two cases.
The capacitor does work to pull in the new dielectric, and this increases the energy stored in the capacitor.
The capacitor does work to pull in the new dielectric, and this has no effect on the energy stored in the capacitor.
The capacitor does work to pull in the new dielectric, and this decreases the energy stored in the capacitor.
The capacitor does no work to pull in the new dielectric since the charge is held fixed.
The increase in energy stored is caused by the friction between the dielectric and capacitor.
Explanation / Answer
New Capacitance, C2 = 7C1
Energy stored by capacitor with increased dielectric, E2 = Q2/2C2 = E1/7
So, energy stored by the capacitor decreases by a factor of seven.
The energy is different because the capacitor does the work to pull in the new dielectric.