Lecture_22

Lecture_22 - Not all radiation must be absorbed – some...

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Expansion, Conduction, Convection, Radiation
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Thermal Expansion A change in temperature can affect many properties of a system – ex. size Linear expansion Volume expansion Δ L L 0 =αΔ T Δ V V 0 =βΔ T
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Examples
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Heat Transfer Conduction – matter-based Convection – matter-based Radiation – not matter-based
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Heat Conduction Q t A Δ T L Examples: Metals feel cold, thermos, windows, preventing ignition/charring
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Convection Transports energy by moving matter, caused by thermal expansion
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Radiation Energy carried by electromagnetic waves Arises from motion of charged particles Higher temperature, more motion, more amplitude. Radiation absorbed by a system will cause the molecules to move more quickly, higher temperature.
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Unformatted text preview: Not all radiation must be absorbed – some can be reflected. Greenhouse Effect The atmosphere allows most of the Sun’s visible radiation to reach the surface It absorbs much of the infrared radiation The Earth radiates in infrared This energy is absorbed by the atmosphere and not released to space The trapped infrared radiation makes the Earth’s surface warmer than it would be without the atmosphere Section 14.8 Blackbody Radiation Blackbodies absorb all radiation – will also be the best radiator of energy Q t =σ e A T 4 Stefan-Boltzmann Law Stefan's Constant Emissivity λ max =( 2.9 × 10 − 3 m ⋅ K )/ T Wien's Law Applications...
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This note was uploaded on 12/07/2011 for the course PHYS 220 taught by Professor Chang during the Fall '09 term at Purdue.

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Lecture_22 - Not all radiation must be absorbed – some...

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