The basic unit that represents the quantum nature of electricity is the charge of the electron, represented with the symbols
, which corresponds to
The quantum nature of electricity was demonstrated for the first time by Millikan, in its oil drop experiment. In this experiment, Millikan put charged oil drops between two metallic plates, applying a potential difference across them, such that the electrical force acting on the drops was in balance with their weight. Knowing the intensity of the electric field and the mass of the drops, he was able to determine the charge of the oil drops, and he found that this charge was always an integer multiple of a certain value, exactly
.