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Energy and Radiation

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Energy and Radiation

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  1. Energy and Radiation Science Concepts Definition Potential Kinetic Radiant Radiation Wave Equation Spectrum Stefan-Boltzmann Law Wein’s Displacement Law Conduction Convection Energy Energy Types Temperature Driven Heat Transport The Earth System (Kump, Kastin & Crane) • Chap. 3 (pp. 34-41; pp. 45-46)

  2. Energy What happens when we drop an object? What happens when water behind a dam spills to the river below? What happens when wood burns? What happens when we turn on a flashlight?

  3. Energy Definition • Energy is the ability to do work - Work = Force • Distance - Units > 1 calorie = energy required to heat 1 gm of water 1°C ‡ Note: 1 Calorie (capital C) = 1000 calories = 1 kilocalorie ◊ Unit for food derived energy Types of Energy • Potential - Chemical > Example: a fire - Electrical > Voltage ‡ Example: a battery uses chemical potential energy to create a voltage and therefore electrical potential energy

  4. Energy (Con’t) Types of Energy (Con’t) • Potential (Con’t) - Gravitational > Result of object's relative position ‡ Example: a falling rock ‡ Example: cold (dense) air (fluid) next to warm (less dense) air (fluid) • Kinetic - Result of an object's motion - Large-scale motion > Example: falling water (hydroelectric power generation) > Example: swinging hammer (drive nail) > Example: air motions, i.e., wind - Micro-scale motion > Example: molecular vibration or temperature. Also called thermal energy

  5. Heat - Energy Transfer “It is like the advent of thermodynamics … in about 1820. They knew there was something called ‘heat,’ but they were talking about it in terms that would later sound ridiculous.” In fact, he says, they weren’t even sure what heat was, much less how it worked. Most reputable scientists of the day were convinced that a red-hot poker, say, was densely laden with a weightless, invisible fluid known as caloric, which would flow out of the poker into cooler, less caloric-rich bodies at the slightest opportunity. Only a minority thought that heat might represent some kind of microscopic motion in the poker’s atoms. (The minority was right.) Waldrop, M.M., 1992: Complexity-The Emerging Science at the Edge of Order and Chaos, Touchstone, pp. 297-298. Types of Energy (Con’t) • Radiant - Example: radiation from a fire in a fireplace - Example: radiation from the Sun Definition • Heat - Energy in transit because of a temperature difference

  6. Heat - Energy Transfer Would walk up and pick up this frying pan? How about this one ? And this one ?

  7. Heat - Energy Transfer Three Mechanisms • Conduction - Objects in contact; molecules bouncing off each other; solids • Convection - Motion; hot air rises; gases and liquids • Radiation - Transfer without requiring a medium; vacuum; Electromagnetic waves

  8. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Conduction - Objects in contact; molecules bouncing off each other; solids - Caused by uneven temperature > Examples: Heat conductivity Material( cal / s - cm - °C ) Air (at 0°C) 0.000058 Air (at 20°C) 0.0000614 Dry soil 0.0006 Dry sand 0.0013 Water (at 10°C) 0.00143 Concrete 0.0022 Wet soil 0.0050 Ice (at 0°C) 0.0054 Steel 0.121 Iron 0.161 Aluminum 0.50 Copper 0.918

  9. Heat - Energy Transfer (Con’t) • Conduction (Con’t) - New fresh, light snow - Good insulator because of trapped air - Older settled or wet snow - Not as good an insulator 1.0 0.9 0.8 0.7 0.6 Snow Density ( g / cm3 ) 0.5 0.4 0.3 0.2 0.1 0 0 0.001 0.002 0.003 0.004 0.005 Conductivity in Snow ( cal / s - cm - °C)

  10. Heat - Energy Transfer (Con’t) Factoid - An oil lamp with a hollow wick burns 10 times brighter than a lamp with a solid wick Three Mechanisms (Con’t) • Convection - Motion; hot air rises; gases and liquids - Caused by uneven heating of fluids - Thermal circulations; Many sizes > Clouds ‡ Convective clouds - cumulus cell > Sea breeze > Monsoon - India and Arizona > Global circulation Effect of convection on flames - Left image (with gravity, i.e., convection) Right image (low gravity in space, i.e., little convection) http://microgravity.grc.nasa.gov/combustion/cfm/cfm_index.htm

  11. Crest Amplitude Height Trough Wavelength Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation - Transfer without requiring a medium; vacuum; Electromagnetic waves - All objects with temperature above absolute zero emit radiation - The analogy of waves is often used to describe radiation

  12. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - The analogy of waves is often used to describe radiation > Wave Equation ‡ Example: Boat dock ‡ Speed of wave = wavelength * frequency or frequency = Speed of wave / wavelength where ( Speed of wave ) for radiation is the speed of light which equals 3 x 108 m / s Frequency Units - RPM - Revolutions / minute Hertz - cycles / sec

  13. Frequency (hertz) Wavelength (m) 23 -14 10 10 Gamma Rays -10 10 18 10 X Rays -6 10 Ultraviolet 14 10 Visible Infrared -2 10 Microwaves 10 10 1 TV 2 10 TV - FM Short-wave 6 10 Broadcast Band 6 10 Long - Wave Radio 2 10 1 Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - Radiation from materials is emitted with a range of wavelengths, i.e., a spectrum of wavelengths “He recognized the model, and knew it was a state-of-the-art microwave protection system. Mounted on each sturdy pole beneath an aluminum hood was a dieletric transmitter and a receiver; a 15 GHz signal was set to one of several selectable AM signal patterns.” Ludlum, Robert, 2002: The Janson Directive. p. 449. NOTE: GHz = gigahertz = 109 Hz

  14. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - Visible range from 0.4 to 0.7 microns NOTE: 10-6 m = m = micron http://observe.arc.nasa.gov/nasa/education/reference/reflect/ir.html

  15. Heat - Energy Transfer (Con’t) Why is a red shirt red? Why is a white shirt white? Why is a black shirt black? Why is a red flame red? Why is a blue flame blue?

  16. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Compare these two statements. Are they correct physics? “The music was so loud, it was almost like no sound, like silence, in the same way that black is every color intensified into nothing.” “K” is For Killer - Sue Grafton (p. 251) “ ‘All colors taken together congeal to whiteness, the greatest part of space is black,’ say the journal notes.” Golf in the Kingdom - Michael Murphy (p. 130)

  17. -6 (10 m) -9 18 10 10 -6 10 14 -5 10 10 13 10 Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - Ultraviolet (uv) C -Shortest wavelength; Most powerful; Filtered by the ozone layer - uv B - Midrange uv; Less powerful; Produces both suntans and burns; Energy dissipated in outer layer of skin; Causes painful burns; Contributes to skin cancer; Do not penetrate glass - uv A - Longer wavelength uv; Penetrates deeply into skin; causes longterm damage; Causes premature aging; Adds to harmful effects of uv B; Can penetrate glass Wavelength Frequency Wavelength (hertz) (m) 0.20 uv C Expanded 0.29 Ultraviolet Ultraviolet uv B 0.32 Wavelengths uv A Visible 0.40

  18. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - Radiation from materials is emitted with a range of wavelengths, i.e., a spectrum of wavelengths (Con’t) Exam Scores 20 18 16 14 12 10 Number of Students per Grade Interval 8 6 4 2 0 0 10 20 30 40 50 60 70 80 90 100 Grades

  19. Visible 17,500  max 15,000 12,500 Emitted Radiation Per Wavelength Interval (Cal - cm-2 - min - mm -1 ) 10,000 7,500 5,000 2,500 0 0.0 0.5 1.0 1.5 2.0 Wavelength ( m) m Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - What is the Sun’s spectrum? > Below is the Sun’s emitted radiation spectrum; assumes the Sun’s outer surface temperature is 6000 K Note: 1 calorie = energy required to heat 1 gm of water 1°C Note: 1 Calorie (capital C; Unit used for food derived energy) = 1000 calories (lower case c) = 1 kilocalorie Note: The Sun emits much of it’s radiation in the visible range with its wavelength of maximum emission, (max), is about 0.48 m, i.e., in the blue-green range 95% of the Sun’s emitted radiation is in the region between 0.25 and 2.5 m

  20. Heat - Energy Transfer (Con’t) Three Mechanisms (Con’t) • Radiation (Con’t) - What is the Earth’s spectrum? > Below is the Earth’s emitted radiation spectrum; assumes the Earth’s surface temperature is 288 K Note: Energy amounts per wavelength interval much smaller than for the Sun Note: The Earth’s wavelength of maximum emission, (max), is about 9.8 m  max 0.050 95% of the Earth’s emitted radiation (gray area) is in the region between 2.5 and 25 m, i.e., at much longer wavelengths Emitted Radiation Per Wavelength Interval (Cal - cm-2 - min - mm -1 ) 0.025 0 30 20 0 10 Wavelength ( m) m

  21. Heat - Energy Transfer (Con’t) Stefan-Boltzmann Law • The Total Radiation per unit area is directly proportional to the object’s absolute temperature to the fourth power, i.e., R = (Const) * T4 = (Const) * ( T * T * T * T ) where T is the temperature in Kelvin and the constant equals 5.67 x 10-8 watts / ( m2 K4 ). Ludwig Boltzmann 1844-1906 http://www-groups.dcs.st-and.ac.uk/ ~history//Mathematicians/Boltzmann.html Josef Stefan 1835-1893 http://www-groups.dcs.st-and.ac.uk/ ~history//Mathematicians/Stefan_Josef.html

  22. Heat - Energy Transfer (Con’t) Stefan-Boltzmann Law • Examples: - For the Sun: T = 6000K R(Sun) = 5.67 x 10-8 W / (m2 K4 ) * ( 6000K )4 = 7.35 x 107 W / m2 - For the Earth: T = 300K R(Earth) = 5.67 x 10-8 W / (m2 K4 ) * ( 300K )4 = 4.6 x 102 W / m2

  23. Heat - Energy Transfer (Con’t) Wien's Displacement Law • Wavelength of the maximum energy times the object’s temperature equals a constant max* T = Const where max is the wavelength of maximum energy, T is temperature in Kelvin and the constant equals 2.89 x 10-3 meter Kelvin. Wilhelm Wien 1864-1928 http://www-gap.dcs.st-and.ac.uk/ ~history/PictDisplay/Wien.html

  24. Heat - Energy Transfer (Con’t) Wien's Displacement Law • Examples: - For the Sun: T = 6000K max (Sun) = Wavelength of maximum energy (Sun) = ( 2.89 x 10-3 m K ) / ( 6000K ) = 0.48 x 10-6 m = 0.48 microns - For the Earth: T = 300K max(Earth) = ( 2.89 x 10-3 m K ) / ( 300K ) = 9.6 microns

  25. Heat - Energy Transfer (Con’t) Summary • Sun emits 1.6 x 105 more energy per area than the Earth emits • The Sun’s energy spectrum is centered in the visible region while the Earth’s energy spectrum is centered in the infrared range • 95% of the Sun’s radiation is in the region between 0.25 and 2.5 microns while 95% of the Earth’s radiation is in the region between 2.5 and 25 microns