Question

1. The filament of a standard 100-W light bulb has a resistance of about 100 ohms. For this laboratory the glass of the light bulb is unfrosted, so that the filament can be viewed directly. The light bulb is connected to a variable AC voltage source (a Variac), which can deliver up to 140 volts AC. When the voltage is low, about 20 volts, the filament is a dull, red color. When the voltage is high, 100 V, how does the filament appear? Explain why. Hint: At a higher filament temperature, photons with higher energies can be emitted in addition to low energy photons 2. When an electron in an atom makes a transition between two energy levels, E and E a photon is emitted. If the photon is in the red portion of the visible light spectrum, what is its wavelength and what is the energy difference between Eve figure in almost any physics text showing the spectrum of colors might be helpful. A useful web site is "What Wavelength Goes with a Color? " at http:/leosweb.larc.nasa gov/EDDOCS/Wavelengths for Colors.html) What are the wavelength and the energy difference for a blue photon? eV Obviously what we mean by "red" is a range of colors. Here you are to estimate the averase wavelength. P-1

Answer 1

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