Answer / premalatha

The way capacitors and resistors behave is totally
different. While resistors allow a current to flow through
them which is proportional to the voltage drop across the
resistor, capacitors oppose a change in voltage across them
by either drawing in or supplying current as they charge or
discharge resp. The flow of current through a capacitor is
thus directly proportional to the rate of change of voltage
across it.

This is given by the relation, i = C* (de/dt) where de/dt is
the instantaneous change in voltage.

As the voltage does not change in the case of DC, de/dt = 0
and the current that is allowed to pass through by the
capacitor is 0. For AC voltage the voltage changes in a
regular manner. Hence here de/dt is not 0 and a current is
allowed to flow through by the capacitor.

Answer / sirish

Also the Capacitive Reactance Xc = 1/(2*pi*f*C)

and as a DC voltage has no frequency associated with it

f = 0

thereby Xc = infinity, and thus is an open to DC.

In a similar fashion for high frequency circuits like RF,
Caps act as a short as Xc tends towards 0.

Answer / jagadheesh

capacitor support alternating voltages only but not constant voltages because capacitance is inversely proportional to the frequency and constant voltages are having zero frequency that means capacitance goes infinity so it does not support constant voltages

Answer / siva krizz

xc=1/c*2*3.14*f
for dc frequencyf=0
therefore xc=infinity and no current flows through it
but for ac there is a particular frequency and the capacitive reactance xc is inversely propotional to it.hence capacitor blocks dc and allows ac and is used in amplifiers to filter dc

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