Electricity is the flow of electrons through a conductor, which is usually copper or aluminum wire. If this flow of atom negative particles is always continuous and running only in one direction, then it is said that it is direct current (DC), which is the electricity generated by batteries. However, if this stream of electrons constantly alternate and reverse the direction, in one way and then the opposite direction, then it is said it is alternating current (AC), which is the electricity we use at home and at industrial plants as it is generated by engine-driven generators at a power plant.
This phenomena is also found in nature, as when a bolt of lightning hits the earth, or jumps and spreads throughout the thunderclouds. In this case, the cloud vapor becomes ionized; in other words, charged with either negative (-) or positive (+) ions. An ion is an atom that has lost or gained an electron, which is a negative particle. If it has lost an electron, then it is a positive +ion; if it has gained one, then it is a negative -ion. Thus, millions of ions contained in clouds will always seek to balance out this difference in charge and find an equilibrium through electrical discharge.
In 1799, the Italian physicist, Alessandro Volta, invented the first battery, which is called the voltaic pile. As mentioned in the first paragraph, batteries generate direct current through ionized electrolytes (molten sodium or potassium). Each one of the electrolyte is put between a copper and a zinc disk (electrodes), which are arranged in a pile, forming cells. Meanwhile, Michael Faraday and Nicola Tesla were the pioneers of alternating current, which is generated when a copper wire is put in a magnetic field that constantly change or alternate the magnet poles. In 1821, Faraday had observed that the rotation of a magnet around a wire and the rotation of the wire around the magnet generated electricity. In 1831, he would discover electromagnetic induction.
Below, the Volta's battery. A source of DC generation
