Electroscope Detecting Charges


What we have here is an electroscope and the electroscope is designed to detect small charges brought near this sphere at the top. It’s electrically connected down to the bottom to the two little gold leaves that are held in place. Gold is very malleable. Those two gold leaves are not worth much because they’re really really really really really thin but they are so thin that they can detect small charges that are pushed down from the top toward the bottom. What happens, we can take a plastic rod and a piece of fur, rub the two of them together. And according to Benjamin Franklin’s original designation, this plastic or his rubber rod would become negative. And so bring this close and you see those leaves separating, and those leaves separate because the negatively charged rod pushes electrons from the top down to the bottom, and leaves those things negatively charged so they do repel each other. And I can touch this to eliminate charge on it by grounding it. So again, negative charge brought near it forces the leaves to spread because it pushes some of the electrons from the sphere at the top down to the bottom. Since it hasn’t touched, there is no conduction. But you can see that there is that action which is often called induction. Same thing will happen if you use Benjamin Franklin’s other concept – the definition of positive is a glass rod rubbed on a piece of silk. Take the glass rod, rub it on a piece of silk and pick up some charge – and it actually loses electrons to make it positive and then bring it near that top sphere and the same thing happens. This pushes – or actually pulls – some of the electrons away from the leaves down at the bottom. And when it pulls electrons away from the leaves those leaves are positively charged and they will repel each other. Now what you can do is test the size of charges and test the sign of the charge if you have this thing charged – the electroscope charged – by a known object. So, negative charged rod, bring it near it, this thing is now charged negatively. You can bring any negative charge near it and it will cause the leaves to spread even more – so you see them going a little farther apart so that’s what a negative will do because it pushes more electrons down. If, however, you bring a positively charged object near it – so charge up that glass rod again, it’s a little bit positive – what it should do is pull some of the electrons up from the electrons in the leaves and you can see that if the leaves go down the object you’re bringing close to it is opposite the charge of the electroscope. The electroscope has been charged positively – or negatively – it has been charged negatively – so that glass rod was definitively positive. You can also take a balloon – take a nice balloon, rub it on your head, and then bring it near, and yeah that’s definitely the same charge so that means the plastic balloon is negative. And then you can take your head and bring your head near it also and see that the hair is the opposite charge. You can also do the same with a piece of tape. So we have a whole roll of tape here and what you do is you take off a piece of the tape and bring that piece of tape near this and and it looks like it has no charge at all. So let me try it again. Looks like it’s negatively charged, and then if you bring the whole thing near it, looks like it’s positively charged. You can also take a big old piece of cloth, it’s nylon, rub it on your head again, that’s negative. And bring your head near it again that would be positive. So it seems that anything that’s like this, like your hair or like the fur, will become positive. And anything that is nylon will become negative. And this electroscope you can use to check it – determine the magnitude of the charge and determine the sign of the charge.

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3 thoughts on “Electroscope Detecting Charges”

  1. Kirtana Sivaraja says:

    thanks 4 the video

  2. mohamud hussien says:


  3. Sindhu Rao says:

    Thanks a lot sir

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