How do circuits work, what are they made of, and who came up with the concept? — RK, New Albany, IN
Circuits themselves are as old as electricity. A circuit is literally a complete loop through which electric current can flow. For example, a flashlight contains a circuit whenever it’s turned on—the current flows from the battery’s positive terminal, through the switch (which is on), through the filament of the light bulb (which glows), and back to the battery’s negative terminal. The battery then gives the current some more energy and sends it around this “circuit” again and again.
But electronic “circuits” are much more modern. Here the word circuit is equivalent to “device,” “board,” or “chip.” Such electronic devices date to somewhere around the beginning of the twentieth century. As radio developed, with tube amplifiers and other electronic components, so did these circuits. Modern electronic systems place many of the components involved in an electronic device on a single sheet of plastic or fiberglass and many of the components on that board may exist on the surface of one or more tiny silicon wafers. These single wafer circuits, called integrated circuits, were invented in 1959 by Texas Instruments and became commercial products at Fairchild Semiconductors in 1965.