Robert Holdsworth, age 12, of Trumbull, C onn., for his question:
What is a voltaic cell?
If you guessed that the voltaic cell has something to do with the volt electrical unit, you are correct. Both are named in honor of Alessandro Volta who made the first voltaic pile. This gadget was the granddaddy of all our electric batteries and it led to the invention of the mighty dynamo. The cell generates electricity by chemical means. The dynamo or generator makes electricity by magnetic means.
Most of our electric power is led by copper wires from the giant generators. But, when machines cannot be plugged into power lines, we use batteries which make electricity from chemicals. In the dry cell usedi say for a flashlight, the moist or pasty chemicals are sealed in a dry container. When more power is needed, say in an auto battery, a number of voltaic cells are arranged to work together.
The early voltaic pile was a pile of zinc and copper discs separated by layers of cloth or leather soaked in lye. Chemical action took place between the discs and the lye solution. When two ends of a loop or circuit of copper wire were attached to the base of the pile, the energy from this chemical action was led off as electric current.
In a modern voltaic cell, two plates connected with wire are placed in a liquid bath. The plates are called the electrodes and they may be one of zinc and one of copper or one of zinc and one of carbon. The bath, usually sulphuric acidp is called the electrolyte.
Chemical action reshuffles the electrons of the molecules in the plates and in the bath. An electron is a charge of negative electricity. A normal atom has an equal number of orbiting electrons and positively charged protons. It is electrically neutral.
But when an atom loses an electron, it is left with at extra charge of positive electricity. We call it a positive ion. When an atom gains an electron, it has an extra charge of negative electricity and becomes a negative ion.
Ions are restless particles. They settle down only when they have regained their negative or positive charges and again become electrically neutral. In the cell, ions form when water mixes with the sulphuric acid. Here and there a molecule breaks into two positive hydrogen ions and one negative sulphate ion. These active ions attack the electrode plates and upset their electrical balance.
The zinc plate loses positive ions and so becomes negatively charged. The copper plate gains positive ions and so becomes positively charged. To become neutral again, it needs the surplus negative charge in the zinc plate. The copper plate attracts these ions and draws them through the connecting wire. This chemical energy is led off as electric current.