CHAPTER 23 - Dispersion of Light. Spectra and the Spectrometer

Abstract

This chapter presents the concepts of dispersion of light, spectra and the use of spectrometer. Newton discovered in the 17th century that white light consisted of a spectrum of colors. If a converging lens of crown glass and a diverging lens of flint glass that have one face with a common radius of curvature are cemented together with Canada balsam, an achromatic combination may be obtained giving a converging element whose focal length is independent of the wavelength of the incident light. If a hydrogen gas discharge tube is used as a source then the hydrogen line spectrum is produced in the field of view of the telescope. A spectrometer can be used to determine the refractive index, for a particular monochromatic light source, of the material of a prism by the accurate determination of the refracting angle of the prism, and the minimum deviation angle for the light. A spectrometer can be used for the air-cell method for finding the refractive index of a liquid.