![]() A “particle ” of light is called a photon, and can be thought of as a bundle of energy emitted by the light source. In the quantum mechanical description of light, the basic tenets of which were developed in the early 1900s by Max Planck and Albert Einstein, light is considered to possess both particle and wave characteristics. It was Newton ’s contemporary, the Dutch astronomer Christiaan Huygens (1629 –1695), who first theorized that light traveled from the source as a series of waves. Interestingly, Newton did not think light traveled as a wave, but rather believed light to be a stream of particles, which he termed corpuscles, emitted by the light source and seen when they physically entered the eye. Therefore, since c is a constant, light waves may be described by either their frequency or their wavelength, which can be interconverted through the relation υ = c/ λ. The speed of light depends on the medium through which it is passing, but, as light travels primarily only through air or space, its speed may be considered to be constant, with a value of 3.0 × 10 8meters/sec. ![]() The frequency of a wave is related to the wavelength and the speed of the wave by the simple relation: υ = c/ λ. The units of frequency are number per second, termed Hertz (Hz). For a light wave traveling at a speed, c, the number of peaks (or troughs) which pass a stationary point each second is the frequency of the wave, symbolized by the Greek letter nu ( υ). The distance between adjacent peaks (or troughs) is the wavelength, symbolized by the Greek A wave is a series of regularly spaced peaks and troughs. Light can be pictured as traveling in the form of a wave. However, both divisions are completely arbitrary as the sound and light spectrum each contain a continuous distribution (and therefore an infinite number) of “colors ” and “notes. He chose to divide the spectrum into seven colors in analogy with the seven fundamental notes of the musical scale. Newton divided the spectrum of colors he observed into the familiar sequence of seven fundamental colors: red, orange, yellow, green, blue, indigo, violet (ROYGBIV). ” A diagram of Newton ’s experiment is illustrated in Figure 1. It was at first a pleasing divertissement to view the vivid and intense colours produced thereby. ‘I procured me a triangular glass prism, … having darkened my chamber and made a small hole in my window shuts, to let in a convenient quantity of the sun ’s light, I placed my prism at this entrance, that it might be thereby refracted to the opposite wall. In a report of his discovery published in 1672, Newton described his experiment as follows: In fact, the word “spectrum ” was coined by Newton to describe the phenomenon he observed. The spectrum of colors contained in sunlight was discovered by Sir Isaac Newton in 1666. The term spectrum is also used to describe the graphical illustration of a spectrum of values. Opposing political parties are often said to be on opposite ends of the (political) spectrum. The masses of fragments from an ionized molecule, separated according to their mass-to-charge ratio, constitute a mass spectrum. Similarly, the distribution of sounds over a range of frequencies, such as a musical scale, is a sound spectrum. For example, sunlight is made up of many different colors of light, the full spectrum of which are revealed when sunlight is dispersed, as it is in a rainbow. The distribution of these values, arranged in increasing or decreasing order, is the spectrum of that property. Certain properties of objects or physical processes, such as the frequency of light or sound, the masses of the component parts of a molecule, or even the ideals of a political party, may have a wide variety of values.
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