How does a capacitor allow AC to pass through it but stop DC?

[mj345]

clamping circuits...mechansim

See i have a problem regarding clamping circuits:
1.what do we mean when we say that "capacitor allows ac to pass through it but stops dc"
2.please see the attachement

 

[berkeman]

See i have a problem regarding clamping circuits:
1.what do we mean when we say that "capacitor allows ac to pass through it but stops dc"
2.please see the attachement

The impedance of inductors and capacitors is frequency-dependent. For capacitors, the impedance is inversely proportional to frequency. So the impedance of a capacitor is infinite at DC, and zero at very high frequencies. The configuration in your diagram is a high pass filter, with low frequencies and DC current not making it through the capacitor, and high frequency currents passing through the capacitor to the resistor.

See the current-voltage relation information for capacitors here, for example:

http://en.wikipedia.org/wiki/Capacitor

.