Brief History of Electronics
1st generation: huge ENIAC type computers, made with by thermionic valves 2nd generation: transistorised computers 3rd generation: silicon chip 4th generation: microprocessors
based on the principle of how heating of a wire in an evacuated glass bulb produces electrons (therm = heat, ion = charged particle), in a valve the negatively charged electroncs driven from the cathode moves rapidly to a more positive anode. the creation of a triode with one more electrode (the "grid") makes it an amplifer of weak signals - making things like radio possible.
radar (radio detection and range finding)
radars are made possible with high-powered thermionic valves - magnetron. this magnetron is more commonly used as the source of microwaves in microwave cookers today. in early radar the magnetron produced high frequency paulses of radio energy that were reflected back from aircraft or ships to reveal their range and bearing.
originally made using germanium, transistors as invented by Bell Telephone Laboratories worked the same way as thermionic valves in that they amplified electrical signals and acted as switches. until the 1950s tho it was not possibile to produce germanium with the high purity required in useful transistors. but once sillicon began to be used in the market as well (replacing germanium as the basic semiconductor for making transistors in the 1960s) then the transistor's price and reliablity and compactness won out over the thermionic valve.
silicon chip consists of hundreds of transistors on a silicon chip linked together to producing a working circuit. it is small light and uses hardly any electrical power compared to the older thermionic valves and transistors from the old days. since the 1970s the number of transistors integrated on a silicon chip has been doubling every few years. circuit complexity has also doubled along with the information processing power.