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# Gold leaf electroscope - how does this "phenomenon" work? Watch

1. Hi everyone,

While experimenting with a gold leaf electroscope, I rubbed a ruler to give it a charge and then touched the metal plate with it. As expected, the gold leaf was repelled by the metal part it was attached to and moved away from it.

I then touched the metal plate to discharge it while keeping the ruler on the plate. The gold leaf returned to its original position because the metal had been discharged; however, when I moved the ruler away from the metal plate, the gold leaf rose and moved away from the metal again. What's more, when I brought the ruler close to/touched the ruler on the metal plate again, the gold leaf was actually attracted to the metal part.

I can't seem to get my head around why the ruler would actually cause the gold leaf to be attracted. Could somebody please explain why this happens?

Thanks!
2. Hi! When you rub the ruler(plastic) using a dusting cloth, you are adding electrons to the plastic material. This causes the plastic to become negatively charged. Next, by placing the ruler onto the metal base, such a zinc, you are adding negatively charged electrons to the zinc metal, causing the zinc plate that is connected to the metal pole inside the chamber that has a gold leaf attached to it to become negatively charged. As a result, both the pole in the chamber and the gold leaf becomes negatively charge right? (Since the negatively charged electrons that are added to the zinc plate are able to move freely throughout the metallic structure of the metal and can flow through the metal pole and the gold leaf.)

Since both the pole inside the chamber and the gold leaf are now negatively charged, since we know that like charges repel, the negatively charged gold leaf is repelled by the negatively charged pole inside the electroscope.

When you remove the ruler and touch the zinc plate, you are removing the electrons that were added to the structure. Both the gold leaf and the pole lose their negative charges to become neutral. The gold leaf will then fall back down from its repelled state.

In this case, the plastic material (ruler) that you used to touch the plate once more actually caused the zinc plate to lose those electrons that were added to it. The gold foil, losing its negative charges along with the pole will cause the gold foil to move towards the pole.

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Updated: January 18, 2015
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