3 ms·

Since the plates attract each other electrostatically -- one is positively charged, the other negative -- it takes energy to pull them apart. The amount depend

• mrfusion 10y ago
  Is there a formula for that? I'm curious now.
  • kmill 10y ago
    CV=Q. Pulling plates apart makes the capacitance C decrease, while the charge Q remains constant. This means V must be increasing. Energy in a capacitor is VQ/2, so the energy increased. (This is somewhat circular reasoning. The point is that the charges on capacitor plates attract each other so it takes work to separate the plates. Integrating the force along the path the plate takes during the separation gives the extra energy stored in the capacitor.) A similar thing is a static generator made using a pie tin. You put a little charge on the pie tin by some means, like rubbing on styrofoam, and then you separate the tin from the styrofoam, which gives more energy to the tin (increases the voltage), which then you can transfer to a Leyden jar. I also discovered in high school that you can use a pair of plastic chairs and two willing participants to generate high voltages when there is low humidity. Person one stands up off the chair, touches person two, then sits down. Person two then stands up off the chair, touches person one, then sits down. Repeat. Eventually, you will generate fairly high voltages that sort of hurt. You can hear the excess static charge on the chair squeal into the atmosphere after standing up.