[Music] hi folks I'm going to show you how to inductively charge an electroscope but in such a way that even when you move the charged object away from the electroscope terminal the foils or Leafs will still repel each other you probably already know that if you hold a charged object like this negatively charged piece of vinyl near the terminal of an electroscope the foils or leaves will repel each other they move apart like this and when you move the charge object away the foils no longer repel each other they move back together like this but to make them repel each other after you move the charged object away there's just one small step you have to add before going into detail on why it works here's a quick demonstration all it takes is your finger at the right time and the right place the key to understanding this is to understand that normally the number of positive and negative charges on the electroscope are equal and they stay equal if there's no charged object around then they're also balanced out everywhere wherever there's a positive charge there's a negative charge to balance it out or neutralize it when we move a negatively charged object near the electroscopes terminal all we're doing is forcing the negative charges away from the terminal and down to the foils and they'll stay there as long as the charged object is around when we move the charged object away the negative charges return to where they were and everything is balanced out or neutral again everywhere that there's a positive charge there's a negative charge to neutralize it but now now let's see what happens if I touch the terminal with my finger while the charge object is near the terminal we start with an equal number of positive and negative charges and everything neutralized we then move the negatively charged object near the terminal and many of the negative charges run away to the foils causing the foils to repel each other but then while still holding the charged object near the terminal I touch the terminal with a finger as soon as I do that the foils come together then when I remove my finger there's no change in the foils and lastly when I remove the charged object the foils repel each other and stay that way they don't come back together let's look at what happened more slowly when I touched the terminal with my finger I added another path for the negative charges to take along my finger into the rest of my body this is called grounding there were still some negative charges on the terminal but they didn't want to join the other ones on the foil because the negative charges on the foil repelled them so for them the repelling force of the negative charges on the charged object was balanced out by the repelling force of the negative charges on the foils so they stayed put but with this new path to take they are repelled to my finger and away my body is pretty big compared to the electroscope so I can handle a small negative charge without making a significant difference to My overall charge balance but now that they're gone the electros scope's terminal is more positive than it was before and that attracts some of the negative charges from the foils up to the terminal some escaped my finger and some remain but now the foils no longer have extra negative charges so the foils no longer repel each other they come together again now with the negatively charged object near by we move the finger away nothing changes as a result but now when we move the charged object away the foils repel each other that's because the finger had removes some of the negative charges from the electroscope there are no longer an even number of positive and negative charges like there were always before when we didn't use a finger so everywhere on the electroscope there are more positive charges than negative charges it's no longer neutral so now the foils are left positively charged and since like charges repel the oils repel each other another interesting thing is that since the electroscope is positively charged when we move the negatively charged object close to the terminal that forces negative charges from the terminal down to the foils potentially balancing out the positive charges and causing the foils to come together instead of apart the last interesting thing to show is what happens when I move a positively charged object near the terminal while the electroscope itself is negatively charged with the foils repelling each other like it is now note that when I rub the vinyl with the glass while the vinyl was became negatively charged the glass became positively charged if I move this positively charged Glass near the terminal that attracts some of the remaining negative charges from the foils up to the terminals temporarily making the foils even more positivly charged and repelling them even further apart this was all a demonstration of charging an electroscope positively using my finger and a negatively charged object a similar sequence of events happens if you charge it using a positively charged object instead and then touch with my finger again just keep in mind the positive charged protons don't move around only the negatively charged electrons do in that case the foils will be left with a negative charge in summary this video demonstrated how to charge an electroscope by induction and in such a way that it stays charged even when we move the charged object away