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10_1425_web_Lec_30_TemperatureEtc

# 10_1425_web_Lec_30_TemperatureEtc - Temperature Expansion...

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Temperature, Expansion, Ideal Gas Law Physics 1425 Lecture 30 Michael Fowler, UVa

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Everything’s Made of Atoms This idea was only fully accepted about 100 years ago—in part because of Einstein’s analysis of Brownian motion . Brown, who studied the sex life of plants, noticed a lot of jiggling pollen grains under his microscope in 1827. He assumed it was because they were alive, but later found the identical jiggling with definitely dead stone powder. This was not understood for half a century….! Applet Movie
Size and Mass of Atoms The hydrogen atom is about 10 -10 m across, others are a few times bigger. Avogadro’s Number: N A = 6.02 x 10 23 , the number of atoms (or molecules) in one gram- mole, 22.4 L volume at NTP. The atomic mass unit is 1.66 x 10 -27 kg . The mass of a molecule in amu = mass of N A atoms in grams: one gram mole of H 2 O is 18 grams. NOTE: this is just a reminder —you should be very familiar with all this from chemistry!

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Clicker Question Assume the molecules Shakespeare breathed out in his last breath (say, one liter) are now uniformly distributed throughout the atmosphere. What is the probability you breathed one in just now, in your most recent breath? A. 1 in 10,000 B. 1 in 1,000 C. 1 in 100 D. 1 in 10 E. More likely than not.
Measuring Temperature We can tell by touch if something is hot or cold, but this is unreliable. The first serious attempt to measure temperature was by Galileo in 1597. A glass bulb has a long thin neck, the end of which is immersed in liquid. As the temperature varies, the gas in the bulb changes volume, sucking up liquid or pushing it down.

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Why was Galileo’s thermometer no good for comparing temperatures from day to day? A. The fluid would evaporate. B. The gas expansion was too small to see
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10_1425_web_Lec_30_TemperatureEtc - Temperature Expansion...

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