Temperature Thermal Expansion Ideal Gas Law Kinetic Theory Heat Heat Transfer Phase Changes Specific Heat Calorimetry Heat Engines

Transcription

1 Temperature Thermal Expansion Ideal Gas Law Kinetic Theory Heat Heat Transfer Phase Changes Specific Heat Calorimetry Heat Engines

2 Thermal Expansion When the temperature of a metal ring increases, does the hole become larger? Smaller? Or stay same?

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4 Thermal Expansion: Linear L L T 0 Coefficients determined experimentally! Volume V V T ~ 3 0

5 Thermal Expansion: Linear

6 Thermal Expansion: Linear The coefficient of linear expansion of steel is 12 x 10-6 / C. A railroad track is made of individual rails of steel 1.0 km in length. By what length would these rails change between a cold day when the temperature is -10 C and a hot day at 30 C? L L T 6 3 L (12 x10 / C)(10 m)(30 C ( 10 C)) 0 L.48m

7 L L T What change in temperature is needed to fill the gap, 1.3 x 10-3 m? 0 brass 19x10 C 23x10 C AL 3 Lbrass LAl 1.3x10 m 3 1.3x10 m T L L brass brass Al Al C

8 Circle Expansion L L T 0 The coefficient of linear expansion of aluminum is 23 x 10-6 /C. A circular hole in an aluminum plate is cm in diameter at 0 C. What is the diameter of the hole if the temperature of the plate is raised to 100 C? 6 (23x10 / C)(2.725 cm)100 C 6.3x10 3 cm d 2.731cm

9 Heat flows from HOT to COLD Conduction (solids) Convection (liquids & gases) Radiation (solids, gases, plasma)

10 The heat Q conducted during a time t through a material with a thermal conductivity k. dt/dx is the Temperature Gradient. P dt ka dx

11 Conduction Problem T L T h c ka A bar of gold is in thermal contact with a bar of silver of the same length and area as shown. One end of the compound bar is maintained at 80.0 C while the opposite end is at 30.0 C. When the energy transfer reaches steady state, what is the temperature at the junction? Ignore thermal expansion of the metals.

12 Hot Air rises, expands and cools, and then sinks back down causing convection currents that transport heat energy. Hot air rises because fast moving molecules tend to migrate toward regions of least obstruction - UP - into regions of lesser density! Rising air cools because a decrease in density reduces number of collisions & speeds decrease. As the air cools, it becomes denser, sinking down, producing a convection current.

13 Uneven heating on the earth and over water cause convection currents in the atmosphere, resulting in WINDS. Global wind patterns (Trade Winds, Jet Streams) are due to convection current from warmer regions (equator) to cooler regions (poles) plus rotation of Earth. Convection Currents in the Ocean (Gulf Stream) transport energy throughout the oceans. Air & Ocean Convection causes the WEATHER.

14 Convection between water and land causes the Winds.

15 Sea Breeze

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19 Stormy Weather When warm air rises, it expands and cools. The water vapor in the air soon condenses into water droplets, which form clouds and eventually these droplets fall from the sky as rain.

20 Windward: Wet Leeward: Dry Cools and condenses at Top Warm Humid Air Pushed Up Warm Dry Air Falls Down

21 High Pressure Dry Warm Weather Low Pressure Stormy Weather

22 Why is Cold Weather So Dry?

23 Why is Cold Weather So Dry?

24 Why is winter cold and summer hot?

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26 Intensity: The Radiation Power, P, passing through an area, A. I P W r m

27 Frequency ~ Temperature When an object it heated it will glow first in the infrared, then the visible. Most solid materials break down before they emit UV and higher frequency EM waves. P 4 e T A Long Short

28 Stefan s Law: 1879 Rate of radiation of a Black Body P = σaet 4 P is the rate of energy transfer, in Watts σ = x 10-8 W/m 2. K 4 A is the surface area of the object Jožef Stefan e is a constant called the emissivity ( ) e varies from 0 to 1 The emissivity is also equal to the absorptivity T is the temperature in Kelvins With his law Stefan determined the temperature of the Sun s surface and he calculated a value of 5430C. This was the first sensible value for the temperature of the Sun. Boltzmann was his student and derived Stefan s Law from Thermodynamics in 1884 and extended it to grey bodies. Copyright 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.

29 A good absorber reflects little and appears Black A good absorber is also a good emitter. P 4 e T A

30 P 4 e T A Radiant heat makes it impossible to stand close to a hot lava flow. Calculate the rate of heat loss by radiation from 1.00 m 2 of 1200C fresh lava into 30.0C surroundings, assuming lava s emissivity is 1. The net heat transfer by radiation is: P e A( T T ) P e A( T T ) (5.67 x10 J / smk )1 m (( K) ( K) ) P 266kW

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32 Assume that the sun is a sphere of radius 6.96 x 10 8 m and that its surface temperature is 5.8 x 10 3 K. a) If the sun is a perfect emitter, at what rate is energy emitted from the surface of the sun? b) What is the rate per square meter at the sun's surface - that is, the Intensity? c)what is the Intensity at which energy is received on Earth in one hour? Ignore effects of absorption due to the atmosphere. The average distance from the Earth to the sun is 1.50 x m. I P 4 r P 4 2 e T A 1370 watts per square meter.

33 The Solar Constant

34 Solar Cycle: 11 year Cycle e-primer_prt.htm

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37 During periods of high activity, the Sun has more sunspots than usual. Sunspots are cooler than the rest of the luminous layer of the Sun s atmosphere (the photosphere). Paradoxically, the total power output of the active Sun is not lower than average but is the same or slightly higher than average. Work out the details of the following crude model of this phenomenon. Consider a patch of the photosphere with an area of m 2. Its emissivity is (a) Find the power it radiates if its temperature is uniformly K, corresponding to the quiet Sun. (b) To represent a sunspot, assume that 10.0% of the area is at K and the other 90.0% is at K. That is, a section with the surface area of the Earth is K cooler than before and a section nine times as large is 90 K warmer. Find the average temperature of the patch. (c) Find the power output of the patch. Compare it with the answer to part (a).

38 Why are cloudy nights warmer than cold nights?

39 The heating effect of a medium such as glass or the Earth s atmosphere that is transparent to short wavelengths but opaque to longer wavelengths: Short get in, longer are trapped!

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41 CO 2 & Temperature Change

42 Impacts of a Warming Arctic The Arctic Climate Impact Assessment, a study commissioned by the United States and the seven other countries with Arctic territory, projects that rising global concentrations of heat-trapping emissions will drive up temperatures particularly quickly at high latitudes.

43 RISING SEAS One of the most important consequences of Arctic warming will be increased flows of meltwater and icebergs from glaciers and ice sheets, and thus an accelerated rise in sea levels.

44 Forrest vs Tundra Caught between rising seas on one side and expanding shrub-filled zones to the south, tundra ecosystems around the Arctic will likely shrink to their smallest extent in at least 100 years, the scientists concluded. This could reduce breeding areas for many tundra-dwelling bird species and grazing lands for caribou and other mammals.

45 1 Meter Rise In Florida

46 ZEPO:A Melting Glacier in Tibet "Thirty years ago, there was no river here. If you come back here in another 30 years, one thing is for sure: There will definitely be no more ice here." -Dr. Yao Tandong, Institute of Tibetan Plateau Research

47 Global Glacial Ice Melting On Kilimanjaro in Kenya, an 11,700-year-old ice cap that measured 4.3 square miles in 1912 had shrunk to 0.94 square miles in 2000, and is projected to disappear altogether in about 15 years. Melting of glaciers in Patagonia has doubled in recent years.

48 Ice Caps Melting in Peru In Peru, the Quelccaya ice cap retreated a rate of more than 600 feet a year from 2000 to up from just 15 feet a year in the 1960's and 70's - leaving a vast 80-foot-deep lake where none had existed when his studies began.

49 It is much too late for sustainable development; what we need is a sustainable retreat. -James Lovelock, The Revenge of Gaia

50 The Gaia Theory The organic and inorganic components of Planet Earth have evolved together as a single living, self-regulating system Life maintains conditions suitable for its own survival. - James Lovelock

51 Our Spaceship Earth One island in one ocean...from space...we re all astronauts aboard a little spaceship called Earth - Bucky Fuller

52 67,000 miles/hr 500,000 miles/hr "We are on a spaceship; a beautiful one. It took billions of years to develop. We're not going to get another. - Bucky Fuller, Operating Manual for Spaceship Earth