Electronics

Electronics, applied science dealing with the development and behavior of devices in which the motion of electrons is controlled. It covers the behavior of electrons in gases, vacuums, conductors, and semiconductors. Its theoretical basis lies in the principles of electromagnetism and solid-state physics discovered in the late 19th and early 20th centuries. Electronics began to grow in the 1920s with the development of radio. During World War II, the United States and Britain concentrated resources on the invention of radar and pulse transmission methods, and by 1945 they had enormous industrial capacity for producing electronic equipment. The invention of the transistor in 1948 as a small, cheap replacement for vacuum tubes led to rapid development in such areas as computers, radio and TV receivers, and sound production and reproduction. Now, with the widespread use of integrated circuits, electronics plays a vital role in communications and industry. All electronic circuits contain both active and passive components and transducers (e.g., microphones), which change energy from one form to another. Passive components are normally conductors and are characterized by their properties of resistance, capacitance, and inductance. Active components are electron tubes or semiconductors; they contain a source of power and control electron flow. Semiconductor diodes and transistors, which are basically sandwiches made of 2 different types of semiconductor, now usually perform the general functions once done by tubes, being smaller, more robust, and generating less heat. Demands for increased cheapness and reliability of circuits have led to the development of microelectronics. In printed circuits, printed connections replace individual wiring on a flat board to which about 2 components per cu cm are soldered. Integrated circuits assemble tens of thousands of components in a single structure, formed directly by evaporation or other techniques as films about 0.03 mm thick on a substrate.