Metr 415/715 Wednesday February

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)

SpectralcalcPetty Radiant emittanceRadiant flux (Wm -2 ) over all wavelengths RadianceRadiant intensity (Wm -2 sr -1 ) over all wavelengths Peak Spectral RadianceMonochromatic intensity emitted at wavelength of maximum emission (Wm -2 sr -1 μm -1 ) Notice that here we must divide by μm Wavelength of peakMonochromatic wavelength of maximum emission (μm) Spectral radiance (refers to the specific wavelength you selected) Monochromatic intensity at the wavelength you specified Band radianceRadiant flux (Wm -2 ) over all wavelengths for the specific “channel” you specified

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

Brightness temperature Described in page , 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

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 × Hz and has a radiant intensity in that direction of 1 / 683 watt per steradian

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

Candelas, lumens and Watts lumen-to-watt.htm lumen-to-watt.htm

Electric Stovetop Burner

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?

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?

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?

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