Chapter 2 Notes

Chapter 2 begins with a look at atomic emission and spectroscopy. Presented below are colour spectra for several common gases:

Figure 2.2.3

The spectra as they appear through a direct-reading spectroscope. Unlike the spectroscope discussed in the chapter in which the user must read the angle at which the spectral line appears and calculate the wavelength this instrument superimposes lines on a backlit wavelength scale. In the above diagram the line spectra for hydrogen (top), mercury, and helium are seen. Only strong lines appear - there may be other weaker lines in the characteristic spectrum of a particular element which simply are not visible here.

Presented below are high-resolution photographs of an actual Franck-Hertz tube employing neon (figure 2.6.3 in the text). These photos, originally shot on 35mm film using a long shutter speed, were digitally enhanced below to make edges more obvious. Clearly visible are the two and three coloured bands of light within the tube. The two 'screens' in the tube surrounding the bands of light are the grids.

Figure 2.6.3 a

Figure 2.6.3 b

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