Energy Loss in Capacitors

Most recent answer: 08/19/2013

Q:
It is widely stated that energy is lost and power dissipated when a capacitor is repeatedly charged and discharged in an AC circuit, for example in a semiconductor logic gate. The power dissipation is reported to be C*V*V*f, where f is the AC repetition rate. This behavior is supposedly associated with the capacitor's "ideal" nature, not ohmic or dielectric losses. I don't understand why this is so; it seems to me that work is done to charge the capacitor, but that the same work is returned to the system when the capacitor is discharged. How can energy be lost in such an ideal system?
- Brian (age 55)
Vermont USA
A:

If the capacitor is 'ideal',  for example two parallel conducting plates, then there is hardly any energy loss except for possible electromagnetic radiation.   However for real life capacitors which have dielectric material that enhances the capacitance there is a so-called dielectric loss.  This occurs because for each field reversal there is a small energy loss in realigning the molecules. See http://en.wikipedia.org/wiki/Loss_tangent.

 

LeeH


(published on 08/19/2013)