functions of capacitors

what are the function of capacitors if:
1. it is in parallel with AC and ground
2. it is in series with AC
3. it is in series with DC
4. it is in parallel with DC and ground (this is the only function of capacitor i know from now, as a bypass capacitor)

thanks

The simple answer: A capacitor will block DC between it's terminals, and pass AC.

If you connect a capacitor with one terminal on ground (earth), and the other terminal to a node that has both a DC and AC voltage, then the AC voltage will be passed through the capacitor to ground, but the DC voltage will remain.

As to answer the four possibilities you listed, I cannot say until I see a diagram of your circuits. (I often get parallel and series confused in my head, and I don't want to lead you astray.)

BEEF 41

http://www.pavouk.comp.cz/hw/en_atxps.html

here is the schematic. look at the input filter from AC. what are the function of capacitors in there?

The capacitor passes AC but its impedance varies with frequency. The higher the frequency, the lower the impedance of the capacitor. The impedance of capacitors is called capacitive reactance, the formula is: Xc=1/2/PI/f/C