What is Current

Chapter Current

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • When most of the charge carriers are electrons, the semiconductor is calledN-type, because electrons are negatively charged. When most of the charge carriers areholes, the semiconducting material is known as P-type because holes have a positiveelectric charge. But P-type material does pass some electrons, and N-type material car-ries some holes. In a semiconductor, the more abundant type of charge carrier is calledthe majority carrier. The less abundant kind is known as the minority carrier.Semiconductors are used in diodes, transistors, and integrated circuits in almostlimitless variety. These substances are what make it possible for you to have a computerin a briefcase. That notebook computer, if it used vacuum tubes, would occupy a sky-scraper, because it has billions of electronic components. It would also need its ownpower plant, and would cost thousands of dollars in electric bills every day. But the cir-cuits are etched microscopically onto semiconducting wafers, greatly reducing the sizeand power requirements.CurrentWhenever there is movement of charge carriers in a substance, there is an electric current. Current is measured in terms of the number of electrons or holes passing a single point in one second.Usually, a great many charge carriers go past any given point in one second, even ifthe current is small. In a household electric circuit, a 100-watt light bulb draws a cur-rent of about six quintillion (6 followed by 18 zeroes) charge carriers per second.Even the smallest mini-bulb carries quadrillions (numbers followed by 15 zeroes) ofcharge carriers every second. It is ridiculous to speak of a current in terms of chargecarriers per second, so usually it is measured in coulombs per second instead. Acoulomb is equal to approximately 6,240,000,000,000,000,000 electrons or holes. A cur-rent of one coulomb per second is called an ampere, and this is the standard unit ofelectric current. A 100-watt bulb in your desk lamp draws about one ampere of current.When a current flows through a resistance—and this is always the case becauseeven the best conductors have resistance—heat is generated. Sometimes light andother forms of energy are emitted as well. A light bulb is deliberately designed so thatthe resistance causes visible light to be generated. Even the best incandescent lamp isinefficient, creating more heat than light energy. Fluorescent lamps are better. Theyproduce more light for a given amount of current. Or, to put it another way, they needless current to give off a certain amount of light.Electric current flows very fast through any conductor, resistor, or semiconductor.In fact, for most practical purposes you can consider the speed of current to be thesame as the speed of light: 186,000 miles per second. Actually, it is a little less.Static electricityCharge carriers, particularly electrons, can build up, or become deficient, on thingswithout flowing anywhere. You’ve probably experienced this when walking on a car-peted floor during the winter, or in a place where the humidity was very low. An excessor shortage of electrons is created on and in your body. You acquire a charge of staticStatic electricity15