A capacitor allow to pass A .C but blocks the D. C why

Question

Why is capacitor contemplated to be a passive device?

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Answer 1

Hello Shashank,

Capacitor is formed by using two metal plates seperated by a dielectric medium .it stores electrical energy.

Capacitor allows to pass ac because -- alternating current is having a periodic sine wave. In India, ac have 50hz frequency.it can be understood mathematically

X= capacitive reactance

X=1/2πfC

f = frequency

C= capacitance

In case of ac f= 50 Hz ,so capacitive reactance have finite value.

But in case of DC ,f= 0 hz ,so capacitive reactance have infinite value.thus it blocks it.

I hope this information helps you

Answer 2

For simplicity let us assume a parallel plate capacitor now when you apply a DC current to that capacitor then after certain time the capacitor flights will gain positive and negative charge change the polarity of the current is not changing the potential drop across the capacitor is same as the direct current and then there won't be any current in the wire connecting the capacitor to the source.

In case of alternating current consider the same parallel plate capacitor once the charges accumulate on the plates of the capacitor and potential draw price across the capacitor and suddenly the change in this polarity of the current happens so the negative plates is now at high potential and positive at lower potential so the current start flowing in the opposite direction and the cycle continues and hands there will be always current flowing through the connecting wires