The Nature of Electricity

The ancient Greeks knew that when a piece of amber is rubbed with wool or fur it achieves the power of attracting light objects. Later on the phenomenon was studied, and the word electric, after the Greek word “electron”, meaning amber was used. Many scientists investigated electric phenomena and during the 19^th century many discoveries about the nature of electricity and of magnetism, which is closely related to electricity, were made. It was found that if a sealing-wax rod is rubbed with a woolen cloth, and a rod of glass is rubbed with a silken cloth, an electric spark will pass between the sealing-wax rod and the glass rod when they are brought near one another. Moreover, it was found that a force of attraction operates between them. An electrified sealing-wax is repelled, however, by a wax rod and also an electrified glass rod is repelled by a similar rod.

The ideas were developed that there are two kinds of electricity, which were called resinous electricity, and that opposite kinds of electricity attract one another, whereas similar kinds repel one another.

UNIT 6

The History of Transistors

Bell Labs is the birthplace of the Transistor, inventing the device that led to a communications revolution.

John Bardeen, Walter Brattain and William Shockley discovered the transistor effect and developed the first device in December 1947, while the three were members of the technical staff at Bell Laboratories in Murray Hill, NJ. They were awarded the Nobel Prize in physics in 1956.

Developed as a replacement for bulky and inefficient vacuum tubes and mechanical relays, the transistor later revolutionized the entire electronics world. The transistor sparked a new era of modern technical accomplishments from manned space flight and computers to portable radios and stereos. Today, billions of transistors are manufactured weekly.

UNIT 7

Semiconductor

A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator; it can vary over that wide range either permanently or dynamically. Semiconductors are tremendously important in technology. Semiconductor devices, electronic components made of semiconductor materials, are essential in modern electrical devices. Examples range from computers to cellular phones to digital audio players. Silicon is used to create most semiconductors commercially, but dozens of other materials are used as well.

Transistors, diodes, integrated circuits and many more devices all have semiconductor technology in common. In terms of electricity there are two main classes of material: namely: conductors and non-conductors (or insulators). From their names it can be gathered that conductors will conduct electricity freely, whereas non-conductors act as insulators preventing the flow of an electric current.

UNIT 8

Radar

In the period before World War II, all the major powers were developing radio location systems. The British concentrated on aircraft detection and location while the Germans developed aircraft navigation systems. These devices operated at meter wave lengths. The invention of the multicavity magnetron by Randall and Root in Britain in 1939 provided the impetus to the development of the centimetre wavelength systems required for modern radar. The disclosure of the device to the U.S. in 1940 was followed by the founding of the Radiation Laboratory. The Radiation Laboratory technical staff grew to more than 1300 engineers and scientists, including ten future Nobel Laureates, and developed more than one hundred models of radar, including early warning systems, anti-aircraft gun-laying radars, anti-submarine radars, ground approach systems, and bomber targeting radars. Other radars were developed at Bell Labs and elsewhere.  Nearly one million radar sets were produced in the U.S. as the war progressed! The Germans and the Japanese also produced a variety of radar systems. However, the Germans never produced the short wavelength systems available to the Allies and were caught in a losing game of technical catch-up.

UNIT 9