For this part, observe the electrically - heated tungsten filament of the light bulb in the desk lamp as the light source.
1. What kind of spectrum do you observe?
2. Does the range of visible light wavelengths from violet to red agree with the range quoted in the Introduction and in physics and astronomy textbooks?
3. Filters are available in a box at the front of the lab. Observe the light source with each of the red, yellow, green and blue filters in front of the slit of the spectrometer. Observe and record the change in the continuous spectrum when each of the filters is used.
The filter plays an analogous role to that of a cool gas between the hot source and the spectrometer, by preferentially absorbing light in a certain range of wavelengths and preferentially transmitting light in the rest of the spectrum of wavelengths.
Each filter can be characterized by the “average” wavelength of the light it passes. The average can be estimated as being located midway between the shortest and the longest wavelengths passed by each filter. What “average” wavelengths would you estimate characterize each of these four filters?
4. The following is done as a joint experiment with the class when the lab lights are turned on.
The temperature of the tungsten filaments in the incandescent lights in the ceiling of the lab will be changed by using a dimmer. Observe and record the effect on the continuous spectrum as the temperature is increased and decreased, keeping in mind the two rules for continuous spectra.