During the gold-foil experiment, alpha rays containing positively charged alpha particles were passed through a thin gold foil. Most rays pass through the gold foil proving that the most part inside an atom is empty. Very few alpha particles could not pass through the foil as those were deflected backward due to the repulsive force of similar charges. This proved the existence of positive charges (protons) in a small region ( at the center of an atom) known as nucleus.