Doubt

i never found it mentioned anywhere while i was studying the capacitance chapter theory.

IN AC circuit current changes diretion continuously form +ve to -ve..

now if we join a capacitor in ac circuit thn continuously +ve and -ve charges occur on the plates and in this way a current is able to flow in circuirt and hence it does work in transferring charges...

where as in dc no current flows in circuit..if capacitor is present so no work is done by capacitor

actually we read it in chapter -alternatin current

i hope u got it...

analyse it by drawing a circuit thn sign of charge we change continously change as current changes it dir..

that is the actual function of capacitors in amplifiers with capacitive feedback.
it works like this.
The capacitor offers infinite resistance to the flow of dc current.
Here is the explanation :

In a dc circuit, frequency is zero.

When current flows through a capacitor the capacitor offers resistance. It is known as capacitive reactance.

Capacitive Reactance X_C = 12πνC

ν = frequency of current
C = capacitance

Since ν for dc current is 0, the equation becomes

X_C = 10 =∞

So the resistance is infinity and hence the capacitor does not allow dc current to pass.

But, in case of ac current, it has a frequency like 50 Hz. So the resistance is finite.