Sunday, November 14, 2004

Lesson 12, 13

ELECTRICITY LESSON 12, 13 – The Voltaic Cell
Lesson: 12, 13.
Take up Hwk: Discussion Questions text 303 #1,2,3,5
Lesson: Voltaic Cell
Overhead of Voltaic cell and note
Demo: of wet cell
Homework: pg. 307 #1-3,4

THE WET CELL



A Voltaic cell is a simple device with which chemical energy is converted into electrical energy. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte (e.g., a dissolved sulfate). If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons). In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell. The voltaic cell is sometimes also called the galvanic cell. The names refer to the 18th-century Italian scientists Alessandro Volta and Luigi Galvani.




The Dry Cell
The most common type of battery used today is the "dry cell" battery. There are many different types of batteries ranging from the relatively large "flashlight" batteries to the minaturized versions used for wristwatches or calculators. Although they vary widely in composition and form, they all work on the sample principle. A "dry-cell" battery is essentially comprised of a metal electrode or graphite rod (elemental carbon) surrounded by a moist electrolyte paste enclosed in a metal cylinder as shown below.






Discarding batteries poses a clear environmental danger. Batteries contain heavy metals, such as silver, nickel, cadmium, lead, mercury, lithium, manganese, and zinc, which can accumulate and concentrate in waterlife, wildlife, and humans. An example of the danger posed by batteries is that one mercury battery contained in six tons of garbage exceeds the allowable limit for mercury in solid waste as established by the federal government.




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