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Thursday , 23 November 2017
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Why Does a Capacitor Allow AC But Blocks DC?

Why Does a Capacitor Allow AC But Blocks DC?

Why Does a Capacitor Allow AC But Blocks DC?

Look at the picture for reference.

I will try to explain this thing in the easiest possible manner. So first of All…

What is a capacitor?

Basically, a capacitor is nothing but 2 parallel metal plates separated by an insulator. The insulator can be anything like paper, air, rubber, plywood, mika, glass anything.

What is the difference between AC and DC?

For this refer to the picture.

As you can see, the voltage value of DC remains constant for all the time the power supply is ON.

But in AC, it is a time varying voltage, This means that for some amount of time it will have a certain polarity but in the next amount of time it will have another polarity. As you will see in the picture, in the column of AC, voltage source V has a certain polarity for time T1 and the opposite polarity for time T2.

Note : T1=T2

What do you mean by charging of a capacitor?

When a capacitor is connected to a voltage source,  then positive charges from the positive terminal of the voltage source and negative charges(electrons) from the negative terminal of the voltage source will travel and GET ACCOMMODATED ON BOTH THE PLATES OF THE CAPACITOR. Refer to the figure in the DC column.

PROPERTY : ONCE THE CAPACITOR IS CHARGED UP TO ITS TOTAL LIMIT, IT WILL ACT AS AN INSULATOR AND WILL NOT ALLOW CURRENT TO PASS THROUGH IT. This is the most important point of the whole answer so read it once again if you haven’t understood it in the first go.

Now we are clear on the basic understandings required for the explanation, I will start the explanation now (don’t worry its not that big) :

DC column of picture :

As you can see, the capacitor gets charged to its total limit when the voltage source charges it. Once charged completely, the holes(positive charges) get accommodated on one plate and the electrons (negative charges) get accommodated on the other plate. So The capacitor gets charged to its total limit and thus doesn’t allow any current to flow, hence DC BLOCKED.

AC column of the picture :

AC IS A TIME VARYING VOLTAGE : The polarity of AC source changes after time T1 and changes again after time T2.

Because of this, for time T1, the capacitor gets charged such that the positive charges are accommodated on the left plate but after time T1, the polarity changes (because the voltage source is AC) and now at the start of T2, the state of the circuit is as follows :

At the time of second half cycle of AC

So now, voltage source V will attract the negative and positive charges from the respective plates to its terminals and current will flow in another direction. And because the capacitor is losing its charges – Capacitor is getting discharged.

After this when once again the polarity will switch (after time T2), the capacitor will again get charged. In this way the capacitor gets charged and discharged again and again and AC current flows through it.

Conclusion:

SO AC CAN FLOW THROUGH A CAPACITOR. NOT LITERALLY THROUGH, BUT BY THE ALTERNATE CHARGING AND DISCHARGING OF THE CAPACITOR, AC CAN FLOW THROUGH IT. DC WILL NOT BE ABLE TO DO SO BECAUSE THE NATURE OF DC VOLTAGE IS TO BE CONSTANT AND THUS CHARGING OF CAPACITOR WILL TAKE PLACE, BUT BECAUSE DISCHARGING WONT TAKE PLACE, DC WILL BE BLOCKED.

Hope you understand this concept. Let me know if you have any questions.

Why Does a Capacitor Allow AC But Blocks DC?

Why Does a Capacitor Block DC But Allows AC?

About Imran Memon

Imran Memon is doing Electrical Engineering From MUET, Started Blogging as hobby, Having Good cammands on Making money online and Blogging you can add him on facebook

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