capacitor basics

Sir, If we touch one terminal of the charged capacitor , is current flow through our body to the ground without any contact with other terminal.

Can you pull a cork out of a bottle one-handed? No you *have* to use the other hand to hold the bottle.

Likewise the capacitor can only push as much current out of one terminal as it pulls into the other.

The only way to reduce the voltage of a so-called charged capacitor is by providing a conductive path between the two terminals of that capacitor.

Earth, or ground is only conductive to other parts of the earth (and rather poorly). People sometimes refer to a common point in a circuit as "ground". A circuit's "common" only has a conductive path to real ground (earth) if it's connected to ground (earth).

Bob

In electrostatics, you can discharge a body by providing a conductive path to earth (or anywhere else); but a capacitor is two charged bodies (plates), holding equal and opposite charges, with an electric field between them. If you connect a conductive path to one plate, only a very small percentage of the stored charge will re-distribute itself.

yes - you put the corkscrew in, tie it to a long piece of string, and then whirl it round very-very-fast... ;)

Sir,

You now have a scientific hypothesis on your hands. Namely that you can discharge a capacitor by touching only one of its terminals to the ground. The thing to do with scientific hypotheses is to test them, so think of a way to do so and try it yourself.

Sir, "current flow" is a misuse of terms, and circuits are circular.

Yabbut, that doesn't work with electrons. (Or, if you're a college boy, raised on "conventional current", the holes. ;-P )

Good Luck! Rich

not unless the other terminal is connected to ground (or to something that connected to ground etc...)

except, some capacitors leak charge but that is a slow discharge process.

Bye. Jasen

If nothing is touching the other terminal no current will flow through the one you touch.

Bye. Jasen

Sir, What is situation in case of lightning .ie lot of electrons are going to ground...could u pls tell me the actual process of lightning ....

In that case, you and the lightning are inside the capacitor, made up of the ground as one plate and the cloud as the other plate, with the air between being the dielectric.

There is a way to reduce the capacitor voltage without a conductive path. You can add more dielectric, which will increase the capacity, and reduce the voltage.

-Bill

Golly! So it is.

You forgot to mention that the capacitor is over its rated voltage when it arcs over. ;-)

Eh? He means increasing the effective area of the plates. Not increasing thickness.

Tim

-- Deep Fryer: a very philosophical monk. Website:

actually, i think it's the other way around but then again, i could be wrong :) i think they actually travel from the ground up and when the path is complete you then get an ionized stream which acts like a short circuit that gives you that nice little light show ect..

That'll increase the voltage unless the dielectric is a gas and the plates aren't moving apart to accomodate the extra dielectric.

to reduce the voltage move the plates closer together.

No, as originally stated, the voltage will *decrease* with "more dielectric".

This is because the dielectric is "stretched" and *that* absorbs energy hence the voltage must drop a little because energy is conserved. See Feynman's Lectures on Physics volume 2 chapter 10 section 3.

Also see chapter 9 for fascinating (non technical) description of lightning.

Cheers Robin