Positive or Negative? How to Find Electric Charge Polarity

Find out if something is positively or negatively charged using just a DIY electroscope. This determines the sign of the electrostatic charge on an electrostatically charged object. The electroscope is first inductively charged from the object being tested. Then a plastic coke bottle is used as an object with known polarity in order to do the test and is triboelectrically charged.

The video showing how to make your own electroscope is:

How inductive charging works video:

The Triboelectric effect video

To follow me on Twitter:

[johndoe-bqxt]

Thank you for referencing the other video on inductive charging. I was used to watching examples of metal blocs being inductively charged that I didn't realize that just by touching the neck of the metal terminal, so close to the actual 'like charged' object that you could ground or move the other like charges from the leaves of an electroscope through you. So, to reiterate, positive screen attracts electrons from the electroscope. Positive charges move to the leaves and repel each other. Then, you touch the terminal, removing the like positive charges from the leaves to the main terminal wire, to your finger, down to ground. The electroscope now has a net negative charge but the leaves are close together again because there's no repulsion because the excess positive charge was removed. Now, the finger is removed and the electroscope is removed and the leaves are repulsed by the excess negative electrons in the leaves and electroscope itself. You bring the charged soda bottle next to the terminal and the leaves 'open - up' some more because they're repulsed even more by the addition of even more electrons from the bottle. I think this is right, is it? Did I explain it right?

[Danzh_]

When I put my hand to the tv and I turned it on I felt a shock

[dalenassar]

THIS WAS A GREAT VIDEO!!!
In all I have seen on electrostatics and the electroleaf, NONE have described how to find the actual +/- polarity of the device that 'spread' the leaves. Now I know that a poly bottle rubbed on our hair leaves it "-". Another one of those 'constants' that it is essential to memorize.
--daLe

[davidomeemo]

your should also make a video about how a neutral object would react. Still good job with this video.

[jeriellsworth]

I like the head rotation shot. :) Great video.

[RimstarOrg]

One way is to spray the charge on by using a high voltage power supply. The output of the power supply would go to a wire with a sharp point and the charge would fly off that point onto the plastic. Another, that's the same as rubbing but doesn't seem like it is to has air flowing over the plastic with charged dust in the air. As the dust contacts and leaves the plastic, it deposits charge. Just a few ideas off the top of my head.

[RimstarOrg]

According to my understanding, and the physics formulas that I know of, no, the attraction force is the same. Coulomb's law, F=kQQ/r^2, doesn't have any preference regarding the signs of the charge when determining the magnitude of the result. However, the ionic mobility of positive ions is less than that of negative ions and that is the cause of a movement in the direction of the positive electrode in some "antigravity" experiments. Maybe that's the origin of the misconception.

[ABC-udju]

But how is tv positively charged as our hair and paper(+charge) gets attracted to the tv plz can someone explain. More over the tv works on cathod ray principal so cathod ray is bombarding the tv screen with electron so it is negatively charge

[RimstarOrg]

When I said it was on the negative scale, I meant that when you rub it with something on the positive scale, then it will become negatively charged. It isn't negatively charged to start with. Being on the negative scale just indicates how it will _become_ charged. There are other ways to charge things, but some things become charged easily by rubbing. Also, we're not naturally positively charged. It's just that when we rub our hair with plastic, our hair will become positively charged.

[RimstarOrg]

Then I would look somewhere other than Coulomb's law being wrong. Another example is that corona discharge differs works differently depending on whether the sharp point is positive or negative. See the wikipedia entry for "Chorona discharge" (about halfway down the page) as another example. The fact that the positive charge is bound in the nucleus and the negative charge is in more mobile electrons leads to differences.

[Bubbletruckwindowcleaning]

Can you do this with water? People say certain kinds of water like distilled are negative charge…

[MagmaSona]

Are your videos for commons creative ? Is there copyright issues if someone uses it for educational purposes ?

[tinkerbit]

The bottle is made of Polyester (PET): Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers;

[RimstarOrg]

I'm guessing the electrons from the electron gun inside the tube are charging the inside of the glass, making the outside positive. I've always heard that the TV tube is a big capacitor. And thanks for your comment that gave me the idea for this video!

[RimstarOrg]

Almost. Your hair isn't positively charged, normally. You hair is at the positive end of the triboelectric series and so if you rub it with something more toward the negative end of the series then it will become positively charged. Luckily, from day to day activity, like combing it with a plastic or rubber brush (plastic and rubber are near the negative end) it often is slightly positively charged.

[TaigiTWeseFormosanDiplomat]

I have no idea that you can learn science from a jar like this.

[wayneschmidt]

Very clear and easily understood video. Thank you!If I may presume upon your time, I have a question about putting an electric charge on ABS plastic. In the description of a Miller gold separating table being sold on Amazon.com, the seller claims that water flowing over a sheet of ABS plastic gives it a positive electric charge, while gold in the same steam acquires a negative charge. As such, the two are attracted. Here's my problem with this claim: First, on every triboelectric chart I've found, ABS plastic is barely on the negative end, just below steel, while gold is halfway down the same chart. Since they are both in contact with the same intermediary material, water, both the ABS and gold would acquire a negative charge. As such they should still repel each other. The ABS is at most less negative than the gold, but note truly positively charged. Second, I don't see how flowing water could charge either material.

It seems to me the seller is misrepresenting the physics of electric charging. I would greatly appreciate your thought on this. Thank you for your time.

[MisterFuturtastic]

I have been studying radiation detectors and I read that they use a quartz fiber covered with gold... do you know what the purpose of using quartz is and why they cover it with gold?

[SIRGAVALOT]

Hi Rimstar could I borrow your mind please. I paint aluminium using a high volume low pressure paint gun. Could you please tell me how to negatively charge the aluminium so that when I spray the paint which I think is positively charged because the air flowing through the hose creates a positive charge. Basically I want the paint I'm spraying to be attracted to the aluminium - how would one achieve this? Many thanks in advance and keep up the good work.

[RimstarOrg]

If you rub hair with something that's toward the negative end of the triboelectric series and make your hair positively charged, then if it attracts something, that something is negatively charged.