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S'està carregant… How Did We Find Out About Electricity? (1973)de Isaac Asimov
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Traces man's knowledge and use of electricity from early Greek experiments to the invention of the telegraph, telephone, and electric light. No s'han trobat descripcions de biblioteca. |
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Google Books — S'està carregant… GèneresClassificació Decimal de Dewey (DDC)537Natural sciences and mathematics Physics ElectricityLCC (Clas. Bibl. Congrés EUA)ValoracióMitjana:
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Detailed review:
Chapter 1: Rubbing and Attracting
Thales of Miletus hears about rocks that stick to iron. When Thales rubs amber it smells nice(!) and it attracts a variety of light things. Once you have magnetism you can make a compass. In 1570 William Gilbert does some magnetic investigations. He calls bodies that attract other bodies when rubbed "electrics", after the Greek word for amber. In 1650, Walter Charleton called this power of attraction "electricity". Otto von Guericke mechanizes rubbing a big ball of sulfur in 1672 and gets some pretty big sparks.
2. Conductors and Non-Conductors
Stephen Gray tries rubbing a hollow glass tube. It attracts stuff too, but when he puts a cork on both ends the corks attract stuff. Woah! Gray experiments to see how far the "electric fluid" will travel along a length of twine. Gray eventually shows that even metals can be given static electricity by rubbing, so long as they are insulated.
3. Fluids and Jars
In 1733 Charles Frances du Fay covers corks with gold foil. He electrifies the gold foil on the insulating corks. If he electrifies just one cork, the two corks attract each other. But if he electrifies both, they repel each other. Then he tries electrifying one cork w/ a glass rod rubbed w/ silk, and the other with a resin rod rubbed w/ wool. Now they attract each other, strongly. Indeed, there are two kinds of electric fluid.
Peter van Musschenbroek (and others) experiment with Leyden jars, a kind of capacitor. He receives a hell of a shock.
4.Positive and Negative
Ben Franklin works the positive and negative theme strongly. Leyden jars can accumulate so much energy because the glass in between the two layers of metal insulates the opposite charges from each other. Franklin realized that lightning is something like the same discharge of electricity that can happen from an electrically charged entity. Franklin does the kite experiment and stores the static electricity passed down from the clouds in a Leyden jar. Leyden jars w/ sharp points can not accumulate electricity. Somehow, this fact inspires Franklin to invent the lightning rod in 1753.
5. Batteries and Generators
This last chapter goes fast.
In 1771 Galvani notices that a spark from a Leyden jar makes a frog leg twitch. He hooks some frog legs to some brass hooks and laid them across the iron grillwork of his window during a thunderstorm, and they twitch. But, they also twitch when the weather is fine. What? The twitching in this case is due to the different metals, brass and iron. Volta makes a "battery" of bowls of salty water connected by strips of alternating tin and copper. He connects a wire between the two ends of this and gets a current flowing. In 1800, William Nicholson splits water w/ electrolysis. In 1807 Humphry Davy enters the fray. In 1819 Hans Christian Oersted discovers that a wire with a current running through it seemed to act like a magnet. In 1829 Joseph Henry winds the wire into coils. Henry makes the first electromagnet. In 1831 Faraday constructs an electric generator. There is a copper plate which just touches a wire at two spots. The copper plate is spun w/in a magnetic field and an electric current is generated. The illustration here is unusually good. Get a steam turbine to spin the wheel and you are converting one sort of power to another and you have an electric generator. Joseph Henry shows how electric current can be used to turn a wheel; the electric motor. Coda: Samuel Morse and the telegraph in 1844. Alexander Graham Bell and the telephone in 1876. The lightbulb in 1879. etc.
THE END ( )