Aparticular solid is electrically charged after it is rubbed, but it is not known whether its charge is positive or negative. how could you determine which charge it has by using a piece of plastic and fur?

You can determine which charge has the solid by rubbing plastic and fur, and bringing near the plastic and the solid to determine if they are repeled or attracted. If they are repeled, the solid is charged negatively and if they are attracted, the solid is charged positively.

Explanation:

In order to determine the charge of the solid (negative or positive) using a piece of plastic and fur, you have to rubb the plastic with the fur (this is charging by friction)

Negative charges are transferred from the fur to the piece of plastic, therefore the plastic is charged negatively.

Then, you have to bring near the solid and the plastic. If them are repeled, it means that the solid is charged negatively (Because similar charges are repeled)

If them are attracted, it means that the solid is charged positively (Because opposite charges are attracted)

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