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Unformatted text preview: 187 Supplement SUPL- 005 Some Comments on Spectroscopy SUPL-005 Th e color of objects has always fascinated human beings. Th e discovery that sunlight can be broken up ( dispersed ) into a spectrum (light of a range of colorsoften described as Red-Orange-Yellow-Green- Blue-Violet) opened up opportunities for both the qualitative and quantitative investigation of color. Th e further discovery that visible light is only a small part of a much broader range of electromagnetic radiation expanded these opportunities to regions to which the human eye does not respond (e.g., ultraviolet light, infrared light, microwave light, etc.). The Properties of Light Spectroscopy is the study of the interaction between matter and electromagnetic radiation . To un- derstand what types of interactions can occur requires knowing the basic properties of electromagnetic radiation. For a long time, light has been characterized in two apparently inconsistent ways. On one hand, it has been thought of as consisting of particles (now called photons) which travel along a path. Th is model has been able to explain many of the properties of light. Some phenomena that light exhibits are di cult to describe with a particle model. Th ese are better understood if light is thought of as a wave. Modern physics tells us that these two models are, in fact, not inconsistent. Indeed, the objects that one usually thinks of as particles, such as electrons, also have wave-like properties. It is entirely appropriate to mix the language of waves and particles. Indeed, the word radiation generally applies to a range of phenomena that includes visible light, X-rays, gamma rays, as well as beta particles and alpha particles. Th e word electromagnetic is used to distinguish radiation in which the particles are photons (which eff ectively have no mass) from radiation consisting of beams of particles that have well-characterized masses (such as the electrons and helium nuclei in beta and alpha rays). Th e electro and magnetic in the word electromagnetic come from the observation that the waves associated with a photon as it travels through space have both electric and magnetic characteristics. Th ese are the basis for the Prepared by R. F. Schneider (Revised 3/09) supplement 005 188 Supplement SUPL- 005 interaction between electromagnetic radiation and matter. We use the word light to include any form of electromagnetic radiationvisible, ultraviolet, infrared, micro- wave, X-rays, gamma rays, etc. What characteristics describe light? Light has a fixed speed (a subtle, and important concept). The speed of light in a vacuum is a universal constant usually designated by the letter c with an approximate value of 3.00 s 10 8 m/sec. The speed can be thought of as applying to both the particle of light (photon) and the associated waves. The waves have a wavelength ( L ) and frequency ( N ) as illustrated in Figure 5-1....
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This note was uploaded on 10/24/2009 for the course CHE 134 taught by Professor Staff during the Spring '08 term at SUNY Stony Brook.
- Spring '08