Question

Why do we say that only repulsion is a sure test of charge on a body?
in short...

Answer 1

we say that repulsion is a sure test of charge in body because we can test charge by only two way one is attraction and second is repulsion. as we know that an charged body attracts non charged body also. for ex. magnet attracts an non magnetic iron but an charged body can give repulsive force to only another charged body