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Metr 415/715

Metr 415/715. Wednesday February 27 2013. Using Spectracalc Program. Be aware of terminology different from Petty’s book Blackbody Calculator tab default value: Temperature 300K Emissivity 1

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Metr 415/715

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  1. Metr 415/715 Wednesday February 27 2013

  2. Using Spectracalc Program • Be aware of terminology different from Petty’s book • Blackbody Calculator tab default value: • Temperature 300K • Emissivity 1 • Recession velocity 0 – (applicable for hot bodies like star moving a great speed with respect to observer) • Wavelength 10 micrometers • Lower and upper limit 8 and 12 micrometers respectively (defining width of spectral band to be calculated)

  3. Color temperature • Temperature that corresponds to the wavelength of maximum emission of a body emitting radiation, regardless of whether the object is a blackbody or not

  4. Brightness temperature • Described in page 125-126, and equation (6.13) • If you know the temperature of a blackbody you know the monochromatic intensity it emits at a particular wavelength • Whether an object is a blackbody or not, if you know the monochromatic intensity it emits at a particular wavelength, you know the temperature a black body would have to have to emit monochromatic radiation if equal intensity at that wavelength • That is called the brightness temperature of the object

  5. Candela • The SI unit of luminous intensity. One candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012Hz and has a radiant intensity in that direction of 1/683 watt per steradian

  6. Lumens • The SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela

  7. Candelas, lumens and Watts • http://www.rapidtables.com/calc/light/how-lumen-to-watt.htm

  8. Electric Stovetop Burner

  9. Using Blackbody calculator from Spectracalc – Step 1 • Black body emitting upward at 300K • Use default settings of Spectracalc (wavelength 10 microns, 8-12 micron band) • What is band radiance (radiant flux)? In what units is it expressed?

  10. Using Blackbody calculator from Spectracalc – Step 2 • Consider a medium through which that blackbody radiation passes that has an absorptivity of 0.3 and a temperature of 250 K • What is band radiance (radiant flux)? In what units is it expressed?

  11. Using Blackbody calculator from Spectracalc – Step 3 • What is total band radiance (radiant flux) received at the top – radiation from black body plus radiation form the medium with 0.3 absorptivity? • What is the brightness temperature of the radiation received?

  12. Setup for next homework set • Do problems: 6.4, 6.5, 6.6, 6.9, 6.10, 6.11. 6.12 • Let’s discuss the givens and what needs to be found • Hint: use Spectralcalc program – it will come in handy

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