Greenwood press
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book-20600
LOGARITHMS
55 tudes, with stars ranked “1” as the brightest. Astronomers using powerful tele- scopes have increased this star-magnitude scale to 29. Analysis of the quantity of light that reaches the viewer indicates that the star-magnitude scale is logarith- mic. In the nineteenth century, the scale was standardized so that a difference of 5 magnitudes corresponds to 100 times greater light intensity. Acidity or alkalinity of a substance is measured on the logarithmic scale pH = –log(H + ), where H + is the concentration of hydrogen ions in moles per liter of the substance. These pH units provide a more compact scale than moles per liter. The scale ranges from 0 to 14, with 7 representing a neutral substance (water). Higher pHs indicate alkalinity, and lower indicate acidic substances. Few plants will sur- vive in soils more acidic than pH = 4 (the acidity of lemon juice) or more alkaline than pH = 8 (baking soda). Battery acid (pH 1) and lye (pH 13) will burn your skin. Litmus papers turn different colors depending on the pH of the substance. A change in color that represents 2 levels of pH will represent a difference of 100 times the concentration of H + ions. The Richter scale is a measure of the strength of earthquakes. An earthquake with a Richter scale value of 4 feels like vibration from a passing train. A scale value of 7 indicates an earthquake that produces ground cracks and causes houses to collapse. Because the scale is logarithmic, the difference in energy from the earthquake waves is 10 7−4 = 1,000. An earthquake measured as a 7 on the Richter scale is 1000 times more powerful than an earthquake measured at 4. Download 1.81 Mb. Do'stlaringiz bilan baham: |
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