lecture22sp08

lecture22sp08 - Lecture 22: Heat and Thermal Properties of...

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Unformatted text preview: Lecture 22: Heat and Thermal Properties of Matter 1 Chapter 16: Quantitative Measures for Sound Speed of Sound in Gases, Liquids, and Solids The speed of sound in air, at standard temperature and pressure, is 344 m/s (see speeds of sound in Table 16.1, page 534). In general for an ideal gas the formula for the speed of sound is Gas: v = v u u t RT M where R is the ideal gas constant which we will see shortly, is a ratio of heat capacities (=1.40 for diatomic gases, =1.67 for the monotonic noble gases), T is the temperature in Kelvin, and M is the molecular weight of the gas in moles. For example, air has an average M = 28 . 8 10- 3 kg/mol, room temperature T = 293 K, and R = 8 . 314 in these MKS units. So the speed of sound in air is v air = v u u t (1 . 40)(8 . 314)(203) 28 . 8 10- 3 = 344 m/s For liquids, the speed of sound depends on the bulk modulus B of the liquid and the density of the liquid Liquid: v = v u u t B For water the speed of sound is 1543 m/s For solids, the speed of sound depends on the Youngs modulus Y , and the density of the solid Solid: v = v u u t Y For steel, the speed of sound is 5941 m/s Intensity of Sound As with energy in any wave, the intensity of sound various with the square of the amplitude of the wave. In the case of sound, there is a dimensionless measure of sound intensity, which essentially is the ratio of a given intensity to the minimum intensity detectable by the human ear. This minimum intensity number is taken as I =10- 12 W/m 2 . The sound intensity (ratio) is called the decibel and is symbolized as . The decibel definition for a sound intensity I is 10 log 10 I I See Table 16.2, page 540, for typical sound intensities Lecture 22: Heat and Thermal Properties of Matter 2 Chapter 17: Temperature and Heat Temperature Temperature is a new physical quantity , for which there are three scales in common use: Fahrenheit (F), Celsius (C), and Kelvin (K, or absolute tempera- ture). These three scales are all related to each other: T F = 9 5 T C + 32 and T K = T C + 273 . 15 Note:- 40 o C =- 40 o F At the atomic or molecular level, we can discover that temperature is a measure of the average kinetic energy in the atoms or molecules. Thermal expansion (see Tables 17.2 and 17.3 on page 578) Solids and liquids will generally expand when the temperature rises. The ex- pansion is proportional to the amount of temperature change according to L = L T and V = L T For solids = 3 . If a solid has linear dimension L , and it is heated but constrained to remain at the same length, then the solid will be under a stress F A =- Y T Liquid volume expansion coefficients are 10 times larger than those of a solid....
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lecture22sp08 - Lecture 22: Heat and Thermal Properties of...

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