There is a very important difference between the property of inductor and capacitor that Inductor block AC but pass DC whereas the capacitor block DC but pass AC. Now, the question is why and how they block or pass AC and DC? In this article, we are going to discuss about it.

## Why Inductor Block AC?

The answer to this question can be given in many ways. Let's find the answer from the below equation. We know that inductor has inductive reactance property by which it opposes the flow of current through it.
The equation of inductive reactance is,

You can see in the above equation, frequency is there. So when we apply AC supply to the inductor, it will oppose the flow of current because as the AC has some frequency, there will be inductive reactance occur.

The opposition by the inductor due to the inductive reactance property is proportional to the supply frequency that means if supply frequency increases the opposition also be increased. For this reason, an inductor can totally block the very high-frequency AC.

## Why Inductor Pass DC?

Now if we apply DC supply to an inductor, the inductive reactance will be zero because the frequency of DC is zero.

So, as the inductive reactance is zero it will not oppose the flow of current. So the inductor passes the DC current, of course, it will offer very small resistance to the flow of current which depends upon the internal resistance of the inductor material.

## Why Capacitor Block DC?

Here also we will find the answer from the equation of the capacitor that is capacitive reactance. Capacitive Reactance is the property of the capacitor by virtue of which it opposes the flow of current.
The equation of capacitive reactance is,

So, according to the above equation if we apply DC supply to the capacitor the capacitive reactance will be indeterminate(we can say very high) because the frequency of DC is zero.

So as the capacitive reactance is very high, the current cannot flow through the capacitor.

## Why Capacitor pass AC?

Now if we apply AC supply to the capacitor, it will pass because AC has a frequency.

The blocking property of the capacitor is inversely proportional to the frequency that means if supply frequency increases, the capacitive reactance decreased so the capacitor will pass more current.