Electricity

[Thnikkaman]

I was wondering, if you took 4 AA batteries, and hooked them up to a metal plate, if it would create a noticiable charge?

[chitrangda]

why don't you try doing.

but i think not a good amout of charge will be produced.

what is the size of metlic strip?

[Iggy]

I was wondering, if you took 4 AA batteries, and hooked them up to a metal plate, if it would create a noticiable charge?

 

No

 

To store a negative charge on a plate you have to load it up with electrons. Simply placing the negative side of a battery on a metal plate won’t force electrons on to the plate. For one thing--a battery doesn’t have a bunch of extra electrons stored up in it to give to something. It needs to pull electrons in through the positive terminal in order to pass them out the negative side.

 

So logically you would wire a plate to the positive side and another plate to the negative side. If you try this (and you should - it’s easy) you could attach the battery between the plates for awhile then disconnect it. Measure the difference in potential between the plates with a voltmeter. Unfortunately, you'll probably notice it didn't store a charge.

 

Last thing you have to do is arrange the plates facing each other and nearly touching. Put a piece of paper between them would be easiest I suppose. Now you’ve got it. Hook the battery up between them... let it charge... remove the battery and replace it with a voltmeter or a light bulb. Voltmeter shows difference in voltage and bulb lights up. You’ve stored a charge. Actually, you’ve made a capacitor (which stores a charge)

 

The reason you have to arrange the plates facing each other is to create an electric field between them. In simple terms, the negative charge on the ‘negative plate’ will reach out and push the electrons out of the ‘positive plate’. It’s really the field between the plates that stores the energy... but we won’t quibble.

[CaptainPanic]

Indeed, 2 plates will work better than 1... because then you make a capacitor. Bigger plate = more electrons stored.

But higher voltage will also store more, so putting the 4 AA's in series will work better than when you put them parallel:

 

[math]Q = C*V [/math]

 

More about capacitors and capacitance on wikipedia.

[Thnikkaman]

Do you mean like this? http://www.scienceforums.net/forum/picture.php?albumid=33&pictureid=283

[Iggy]

Do you mean like this? http://www.scienceforums.net/forum/picture.php?albumid=33&pictureid=283

 

Put the batteries in series and arrange the plates facing each other and almost touching, like this:

 

 

Put something non-conductive between the plates (like paper) then sandwich them together. It won't work great, but it will work.

Edited August 25, 2008 by Iggy

[alan2here]

When I opened an old capacitor with scissors I noticed its internal structure was like that of a cylindrical onion.

 

Could I presume from this that many rings of foil separated by rings paper would be better?

 

Or that many layers of foil separated by layers of paper or if possible tracing paper would be better?

 

Would touching the plates once they are newly charged in the above example give a small static shock or DC electric shock? If so how much power would be needed to feel anything?

 

How long does the capacitor hold charge or alternatively at what rate would it loose charge?

 

presumably more batteries in sequence as in the above example = more charge for longer?

 

I could imagine three low viscosity liquids of differing weights two of which are very electrically conductive and one of which is highly electrically insulative where only a tiny amount of the middle layer was used forming a very actuate extremely small gap?

Edited August 31, 2008 by alan2here

[big314mp]

Capacitors are actually spiral wound, rather than in layers like an onion. It's done to get more area in a smaller package. So to build one, you would have a very long strip of foil-insulator-foil-insulator layering, and then roll the whole thing up. A wire attached to one foil strip would be one terminal, and a wire attached to the other foil strip would be the other terminal.

 

If you are familiar with fruit by the foot candy, it is sort of that structure, except doubled (i.e. paper, candy, paper, candy as opposed to just paper, candy).

 

Static tends to be in the kilovolt range, whereas with 4 AA batteries you would only get ~6V of potential.

 

You can take a look at leyden jars and beer bottle capacitors for building a high voltage capacitor, and then hooking it up to an electrostatic generator, such as a Van de Graaf machine, or a Wimshurst machine (if you can find one). If you do this, be very careful as a sizable capacitor/electrostatic machine combo can deal a very nasty punch.

 

I should mention that the foil strips can't touch each other, otherwise the thing would short out internally.

[alan2here]

Best I have is a large battery pack (containing 10 prob A batteries) makes sparks when you rub the ends of the wires coming out of it together.

 

Why would a beer bottle capacitor be better than a spiral foil-paper-foil capacitor?

[big314mp]

I should have clarified.

 

A beer bottle capacitor is for high voltage (i.e. the static you were referring to) as the dielectric (the insulator) doesn't break down under high voltage. I suggested it for collecting static electricity, rather than powering it from a battery.

 

and don't forget...foil,paper,foil,paper. That second strip of paper has to be there. And some electrical tape to make a case for the outside would be good.

 

Have fun! And post back results!

[alan2here]

Thanks :¬)

 

It's nice to know about how to do it. But I don't have voltage measuring kit and the such. I prob won't build it just yet.

[CaptainPanic]

A voltage measuring kit (multimeter or a multitester, also known as a volt/ohm meter or VOM) is cheap, and can be bought in a lot of shops that sell electronic components. It's not expensive (though I haven't looked for one for some time, I expect they cost less than 15 euro).