Question

there are two kinds of charges. how do we know this?

Answer 1

there are two kinds of charges positive and negative and we can know that by
positive charge-
when the glass rod rubbed with silk cloth
negative charge-
when the ebonite rod rubbed with the fur
these are two kinds of charges which can repels

Answer 2

There are two kinds of charge in nature and they are Positive and negative.
Glass rod and silk cloth rubbing experiment shows the exchange of charge.
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