originalstate. An automobile battery, called a lead-acid battery, is secondary. The simplest arrangement of parts that will produce current is called acell. A battery combines two or more cells to produce higher voltage or morecurrent. Connecting the cells in series increases the voltage. Connecting them inparallel raises the current, or amperage.A very simple form of cell is one called a voltaic cell, in honor of Volta. It uses astrip or rod of copper, another of zinc, and sulfuric acid mixed with water. Thepieces of metal are called electrodes. The solution is called the electrolyte. Thecopper electrode is the cathode, or positive electrode, because it has a positiveelectric charge. The zinc electrode is the anode, or negative electrode,because it has a negative electric charge.When the cell is not in use, the molecules of the acid in the electrolyteseparate into electrically charged portions called ions. In chemical symbols, thismeans the sulfuric acid electrolyte (H2SO4) dissociates into two positivelycharged hydrogen (2H+) ions and one negatively charged sulfate ion (SO4=).Note that the sulfate ion has a double negative charge, indicated by the twominus signs. The copper electrode can start electric current flowing as soon as itis connected outside the cell to the zinc electrode. It can do this becausecopper attracts electrons, which make up the current, more strongly than zincdoes. The copper electrode cannot attract electrons through the electrolyte,however, because electrons have a negative electric charge like the sulfateions. The negative charges repel each other, and this stops the flow of electrons.Once the copper electrode starts drawing electrons through an externalconnection, a chemical reaction helps to keep the current going. Every zincatom that loses electrons to the copper electrode becomes a zinc ion (Zn++)with a double positive charge. Sulfate ions promptly attract the zinc ions into thesolution where they combine...
