NATS 1840 Lecture Notes - Wide-Body Aircraft, Clothes Dryer, Kilowatt Hour

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20 Nov 2012
Department
Course
Professor
Science, Technology and the Environment (SC NATS 1840A) - Tuesday
October 23rd, 2012
READING: CH 3.4, 3.7
Heat and Electromagnetic Radiation: Intimately connected in a manner crucial to understanding climate
and climate change.
Example: A rock is exposed to sunlight. Its surface absorbs E.M. energy continuously. It is going to
absorb some of the energy from the sun and as it does so, but how does this absorption mechanism
work, you have to think about the atoms that make up the rock. Through conduction the temperature
increases due to the E.M. energy being absorbed.
Molecules’ average speed increases.
Thermal energy (temperature) increases.
Why does the rock not eventually melt?
Motion of molecules causes emission of E.M. Radiation.
Rock loses thermal energy in E.M. form at the same time as it absorbs it.
Frequency of emitted ration determine by object’s temperature.
The Object “glows
Radiation Equilibrium
Constant temperature (steady state) reached when
(Total energy absorbed)/sec = (Total energy radiated)/sec
No further net energy build-up in the object.
At night no energy is absorbed, but rock continues to “glow” (lose energy) due to thermal content. It
cools
All objects glow in this way. Average frequency of glow increases with object’s temperature.
“Glow” is distributed over a range (spectrum) of frequencies, with the peak determined by
temperature.
Units of Energy and Power:
Energy: Metric unit is the Joule (J). 1 J = 4.18 calories (cal)
1 Calorie = Energy needed to raise temperature of 1 gram of water 1 degree Celsius.
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