Electromagnetic radiation visible spectrum

FIGURE 19-39 Electromagnetic radiation. The spectrum of electromagnetic radiation, and the energy of photons in the visible range of the spectrum. One einstein is 6 X 1023 photons. 

Emission of electromagnetic radiation in the visible and ultraviolet regions of the spectrum by atoms and ions after electronic excitation in electrical discharges. 

A spectrum is a plot of some measure of the electromagnetic radiation absorbed by a sample versus the wavelength or energy of the electromagnetic radiation. For example, it is common practice to plot the absorbance versus wavelength for spectra in the ultraviolet and visible spectral regions as shown below (Fig. 5.1). 

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