The tungsten filament of an incandescent light bulb hasatemperature of approximately 3000 K. The emissivity of tungstenisapproximately 1/3, and you may assume that it is independentofwavelength.
(a). If the bulb gives off a total of 100 watts, what is thesurfacearea of its filament in square millimeters?
(b). At what value of the photon energy does the peak in thebulb'sspectrum occur? What is the wavelength corresponding to thisphotonenergy?
(c). Sketch the spectrum of light given off by thefilament.Indicate the region on the graph that corresponds tovisiblewavelengths, between 400 and 700 nm.
(d). Calculate the fraction of the bulb's energy that comes outasvisible light. (Do the integral numerically on a calculatororcomputer.) Check your result qualitatively from the graph ofpart(c).
(e). To increase the efficiency of an incandescent bulb, wouldyouwant to raise or lower the temperature?
(f). Estimate the maximum possible efficiency (i.e. fractionofenergy in the visible spectrum) of an incandescent bulb, andthecorresponding filament temperature. Neglect the fact thattungstenmelts at 3695 K.
The tungsten filament of an incandescent light bulb hasatemperature of approximately 3000 K. The emissivity of tungstenisapproximately 1/3, and you may assume that it is independentofwavelength.
(a). If the bulb gives off a total of 100 watts, what is thesurfacearea of its filament in square millimeters?
(b). At what value of the photon energy does the peak in thebulb'sspectrum occur? What is the wavelength corresponding to thisphotonenergy?
(c). Sketch the spectrum of light given off by thefilament.Indicate the region on the graph that corresponds tovisiblewavelengths, between 400 and 700 nm.
(d). Calculate the fraction of the bulb's energy that comes outasvisible light. (Do the integral numerically on a calculatororcomputer.) Check your result qualitatively from the graph ofpart(c).
(e). To increase the efficiency of an incandescent bulb, wouldyouwant to raise or lower the temperature?
(f). Estimate the maximum possible efficiency (i.e. fractionofenergy in the visible spectrum) of an incandescent bulb, andthecorresponding filament temperature. Neglect the fact thattungstenmelts at 3695 K.
