Late-nineteenth-century scientists found that the positions of the lines obeyed a pattern given by the following equation: Particularly simple was the spectrum of hydrogen gas, which could be described easily by an equation no other element has a spectrum that is so predictable (Figure 8.04 “Hydrogen Spectrum”). Why does the light emitted from an electrically excited gas have only certain colours, while light given off by hot objects has a continuous spectrum? For a long time, it was not well explained. Here are the colours of light in the line spectrum of Hg. (b) However, when electricity is passed through a gas, only certain colours of light are emitted. Figure 8.03 “Prisms and Light.” (a) A glowing object gives off a full rainbow of colours, which are noticed only when light is passed through a prism to make a continuous spectrum. It turns out that every element has its own unique, characteristic line spectrum. However, when electricity is passed through a gas and light is emitted and this light is passed though a prism, we see only certain lines of light in the image (part (b) in Figure 8.03 “Prisms and Light”). This image is known as a continuous spectrum. We notice this when the visible portion of the electromagnetic spectrum is passed through a prism: the prism separates light into its constituent colours, and all colours are present in a continuous rainbow (part (a) in Figure 8.03 “Prisms and Light”). Incandescent lights and fluorescent lights generate light via these two methods, respectively.Ī hot object gives off a continuum of light. There are two fundamental ways of generating light: either heat an object up so hot it glows or pass an electrical current through a sample of matter (usually a gas).
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