An electrical property of particles, such as electrons and protons, which causes them at a given time to attract and repel each other. A material with an excess of electrons is defined to have a “negative” charge. They are also called N-type. In the reverse, material with an absence of electrons or an excess of protons is defined as “positive” or P-type. Materials with a balanced number of electrons and protons are called “neutral.” Positive and negative charges attract each other. That attraction can cause interesting effects at the junction between positive and negative semi-conductors. This special junction is what makes the right configuration of semi-conductors work as a transistor or a diode.