SKEDSOFT

Capacitors used for ac must be unpolarized so they can handle full voltage reversals. They also need to have a lower dissipation factor than capacitors used as dc filter capacitors, for example. One important application of ac capacitors is in tuning electronic equipment. These capacitors must have high stability with time and temperature, so the tuned frequency does not drift beyond some specified amount.
Another category of ac capacitor is the motor run or power factor correcting capacitor. These are used on motors and other devices operating at 60 Hz and at voltages up to 480 V or more. They are usually much larger than capacitors used for tuning electronic circuits,

and are not sold by electronics supply houses. One has to ask for motor run capacitors at an electrical supply house like Graingers. These also work nicely as dc filter capacitors if voltages higher than allowed by conventional dc filter capacitors are required.
The term power factor PF may also be defined for ac capacitors. It is given by the expression