Capacitor

Hello IngEli

This Topic should really be in: http://cr4.globalspec.com/section/electrical-engineering

and I have asked Admin to move it there.

When a capacitor is in series with an AC voltage source, the plates charge up, discharge, charge to the opposite polarity repeatedly, at the same frequency as the supply voltage.

Because the effort of charging and discharging, changing polarity of voltage on the plates is repeated, an AC Ammeter is able to sense the effect of the electons in that circuit surging back and forth.

The electrons do not really move very much, like waves in water where the water molecules just travel in small circles but remain essentially in the same place, so it is with the electrons in the connecting wires and the capacitor.

A similar condition to a shock wave in air, where the air molecules are shocked into passing the sound, although most air molecules remain almost in the same place.

I trust that assists your understanding of AC current "through" a capacitor.

Refer further here: http://physics.bu.edu/~duffy/PY106/ACcircuits.html

Kind Regards....

Hello,

Current do not passes in both the cases like in a Resistance connected to a battery.it is only migration of electrons from +Ve plates to -ve plate.

And it happen in the case of both AC and DC, the only difference is that, it happen only once in case of DC and happen repeatedly in case of AC. As the change of polarity at a given frequency is the very first characteristic of AC.

Hi InqEli. The other guys have already told you what really happens in the case of a capacitor. The issue is this: it looks like that the current passes through a capacitor, but it doesn't. When you charge a capacitor with a dc voltage, electrons enter the one plate (coming from the wire connected to this plate) and correspondingly other electrons exit the other plate (entering the wire connected to this plate). So, if you look at the capacitor's terminals: it looks like that the electrons go into the one terminal, pass through the capacitor and come out from the other terminal of the capacitor. But, as you can see, this "current flow" through the capacitor is only apparent and not real. And this current flows just for a while (i.e. until the capacitor is fully charged or discharged). In the case of AC current we have a continual charging and discharging of the capacitor thus it "seems" that we have a continuous current flow through the capacitor. But, of course, in both cases (DC and AC operation) no current is actually passing through the capacitor.

Here's another analogy which might help. Imagine a large sheet of plastic covering a hole in a wall (this is the "equivalent" to the dielectric between the plates of the capacitor). Turn on a speaker ("AC") at one side of the sheet and you will clearly hear it at the other side; turn on a fan ("DC") at one side and you will not feel the breeze at the other side.

Take 2 glasses, each filled half way with water. Pour one into the other until one is full. Now reverse the process and pour from the full into the empty, and back and forth........ this is ac current in a capacitor, how often you pour from one to the other is the frequency. One glass is the anode, the other the cathode. (not to confuse, but the really only charges forward bias, reverse bias just discharges the cap back to the original conductor/wire)

Take an empty glass and place it under the running faucet. This is dc. The glass will fill until it is full and then no more water can flow in until the source is shut off and the capacitor / glass emptied.

questions like this... waste my time just reading....

look... know what you know...and...KNOW what you don't know!

go look it up your self... very fundimental electronic theory and/or a physics book

if the time you'd spent typeing this in, was used to look it up in wikipedia or a text book...

most importantly to get through life... KNOW what you don't know... so you stop BS'n the rest of us!!!!!

Reactance of capacitor=(1/jwc)

j=imaginary number

j=square roots of (-1)

w=angular frequency

w=2×∏×f

∏=3.1428

f=frequency

c=capacitor value

As we know DC current has a zero value of frequency i.e, value of current never becomes zero after a fixed interval of time i.e, its value is always fixed. So reactance offer by capacitor is always infinite value. Capacitor works as open circuit. So no current can pass through capacitor.

But AC current has some value of freuency, so reactance offer by capacitor is always finite value. So current always pass through capacitor.