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If a parcel of air has a constant temperature and does not move…

If a parcel of air has a constant temperature and does not move… a. ...its pressure and temperature are higher than the of the surroundings b. ...its pressure and temperature are lower than the of the surroundings c. ...its pressure and temperature are equal to those of the surroundings.

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If a parcel of air has a constant temperature and does not move…

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  1. If a parcel of air has a constant temperature and does not move… a. ...its pressure and temperature are higher than the of the surroundings b. ...its pressure and temperature are lower than the of the surroundings c. ...its pressure and temperature are equal to those of the surroundings Thermal equilibrium

  2. Heat transport by Radiation Radiation

  3. What sort of radiation is this?What are its properties?

  4. Aspects to explore: Interaction with atmosphere Reflection scattering transmission Re-emission absorption Source: Blackbody radiation

  5. Electromagnetic radiation Fig. 2-6, p. 34

  6. The electromagnetic spectrum Fig. 2-7, p. 34

  7. All objects emit radiation if their temperature is not absolute zero. (1)

  8. The sun emits visible light. T=6000 K

  9. The Earth emits infrared radiation into space, T=290 K

  10. Even space emits radiation in the Microwave range, T= 3K

  11. The electromagnetic spectrum Fig. 2-7, p. 34

  12. The electromagnetic spectrum - light Infrared light: Far IR = 300 m Near IR = 0.7 m Visible light: wavelength = color Red = 0.7 m Violet = 0.4 m Ultraviolet light: Near UV = 0.4 m far UV = 0.00003 m Fig. 2-7, p. 34

  13. Stefan-Boltzmann Law The higher the temperature, the higher is the intensity of the emitted radiation. Intensity = energy per time and area Intensity = 5.6710-8 T4 (joule per second and m2)

  14. Black body radiation balance of a human body? • Skin temperature 35oC • Surface area 2 m2 • Room temperature 20 oC

  15. 2900 Wavelength of maximum Radiation = Temperature of object Wien’s Law The higher the temperature of the blackbody, the smaller is the wave length of the emitted radiation.

  16. 2900 Wavelength of maximum Radiation = Temperature of object 2900 Wavelength of body Radiation = = 9.4 m 308 Your body’s radiation: • T=35 C = 308 K • Wien’s Law: Infrared light: Far IR = 300 m Near IR = 0.7 m

  17. Infrared light: Far IR = 300 m Near IR = 0.7 m Visible light: wavelength = color Red = 0.7 m Violet = 0.4 m Ultraviolet light: Near UV = 0.4 m far UV = 0.00003 m

  18. Fig. 2-8, p. 36

  19. Summary of radiation laws (1) All objects emit radiation if their temperature is not absolute zero. (2) Stefan-Boltzmann Law: The higher the temperature, the higher is the intensity of the emitted radiation. (2) Wien’s Law: The higher the temperature, of the blackbody, the smaller is the wave length of the emitted radiation..

  20. Why is there no frost under the trees?

  21. The electromagnetic spectrum Infrared (IR)

  22. The electromagnetic spectrum Ultraviolet (UV) Infrared (IR)

  23. The electromagnetic spectrum X rays Infrared (IR) Ultraviolet (UV)

  24. The electromagnetic spectrum Radio waves, Radar and microwaves Infrared (IR) X rays Ultraviolet (UV)

  25. Increasing wave length The electromagnetic spectrum Ultraviolet (UV) Radio waves, radar and microwaves Infrared (IR) X rays

  26. Increasing wave length Increasing energy The electromagnetic spectrum Ultraviolet (UV) Radio waves, Radar and microwaves Infrared (IR) X rays

  27. The electromagnetic spectrum 0.4 m 1 m 0.7 m 0.00003 m 300 m Ultraviolet (UV) Radio waves, Radar and microwaves Infrared (IR) X rays

  28. The electromagnetic spectrum Terrestrial radiation Solar radiation 1 m 0.4 m 0.7 m 300 m 0.00003 m Ultraviolet (UV) Radio waves, Radar and microwaves Infrared (IR) X rays

  29. The electromagnetic spectrum 280 K 5800 K Terrestrial radiation Solar radiation 1 m 0.4 m 0.7 m 300 m 0.00003 m Ultraviolet (UV) Radio waves, Radar and microwaves Infrared (IR) X rays

  30. Emissions of a blackbody Use the applet “energy curves” to review • Stefan-Boltzmann Law • Wien’s Law

  31. Radiation interacting with a surface Sun light 100 % Reflected fraction x Moves away, and does Not change the object Changes the internal energy Of the object (often temperature increase Or phase transition) Absorbed fraction Object: clouds, air, Surface, ocean, … Note: only absorbed radiation changes the temperature of the Object! Transmitted fraction Moves away, may have been modified by the object

  32. Radiation interacting with a surface Albedo: reflectivity of a surface, x High Albedo: Low absorption Low Albedo: high absorption

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