How can you show there are two kind of charges positive and negative ...
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 repel
EXAMPLE: Let us suspend two pith balls as shown in figure(a). A glass rod after rubbed with silk or woolen cloth is touched to the pith balls.
We will observe the pith balls are getting repelled. Similarly, an ebonite or plastic rod is rubbed with fur is touched to the pith balls.
We again observe there is a repulsion between the pith balls as shown in figure (b). When a pith ball is touched with a glass rod after rubbing
with silk and another pith ball is touched with plastic rob rubbed with fur, we observed the two pith balls attract each other.
This experiment shows that (i) only there are two kinds of charges, we call it as they are +(positive) and -(negative).
(ii) similar charges repel each other, but opposite charges attract each other.