Think of Rutherford's experiment. Most alpha particles passed straight through, but a few were repelled so strongly that they were bounced back or deflected at large angles. This led Rutherford to conclude that the charge of the nucleus of an atom must be... what?

Rutherford considered these observations and he concluded: The fact that most alpha particles went straight through the foil is evidence for the atom being mostly empty space. A small number of alpha particles being deflected at large angles suggested that there is a concentration of positive charge in the atom.

Hope it helps

current flows in a wire