Modern Physics

The spectrum of elements

Schematic of a spectrometer for determining the frequencies present in the light emitted by a hydrogen spectral lamp

As we have already seen in the study of Optics (dispersion of white light), when a beam of polychromatic light falls on a glass block or prism, we observe that the light, when refracted, decomposes into different colors. The set of colors that make up a polychromatic light is called the spectrum of light.

For a long time, attempts have been made to explain the colors emitted by the hydrogen spectral lamp. This lamp is made with a glass ampoule containing hydrogen at low pressure, through which an electric current passes. When they suffer collisions with the electrons of the electric current, the atoms of the lamp absorb energy and begin to emit light.

 we see how the light emitted by the hydrogen lamp was analyzed. The light from the lamp entered the spectrometer through a small slit and was dispersed by light waves. A photographic film, placed after the prism, recorded the intensity of all frequency components present in the light.

Surprisingly, the hydrogen lamp did not have a continuous distribution of frequencies, but just a set of streaks of different colors. This set of rays is known as the spectrum of hydrogen .

Studying other elements, such as helium and noble gases, it was discovered that each of them generated a different and characteristic spectrum.

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