The tungsten filament of an incandescent lightbulb has a temperature of approximately 3000 K. The emissivity of tungsten is approximately 1/3, and you may assume that it is independent of wavelength.
a) If the bulb gives off a total of 100 Watts, what is the surface area of its filament in square millimeters?
b) At what value of the photon energy does the peak in the bulb’s spectrum occur? What is the wavelength corresponding to this photon energy?
c) Sketch the spectrum of light given off by this filament. Indicate the region on the graph that corresponds to visible wavelengths, between 400 nm and 700 nm.
d) Calculate the fraction of the bulb’s energy that comes out as visible light. Check your result from part c.
e) To increase the efficiency of an incandescent bulb, would you want to raise or lower the temperature?