Question

There are two kinds of charges how do we know this?

Answer 1

There are various examples that depict the presence of two charges ( positive and negative)

The charge on an electron repels the charge on another electron but attracts the charge on a proton...

Though the charges on an electron and proton have the same strength, They are of two different natures.

The net charge on an electron-proton system seems to be zero.

It is therefore convinient to define one charge as positive and other as negative

And , Hence we know that there are two kinds of charges

Those positive amd negative are arbitrary things but still, We carry on with them due to Benjamin Franklin!!

Thanks

Hope it helps!!