光（光学）定义单位和光源

　　英语阅读系列第2篇光   （本文仅适合中学生阅读科技类文本）
　　内容: 物理 Physics
　　正文: 1115个单词 Text: 1115 words
　　Title: Light (Optics): Definition, Units & Sources
　　标题: 光（光学）:定义、单位和光源
　　Understanding light allows us to understand how we see, perceive color and even correct
　　our vision with lenses. The field of   optics  ​ refers to the study of light.
　　了解光可以让我们了解我们如何看待、感知颜色，甚至用镜片矫正我们的视力。光学领域是指对光的研究。  What Is Light? 光是什么？
　　In everyday speech, the word ＂light＂ often really means ​  visible light  ​, which is the type perceived by the human eye. However, light comes in many other forms, the vast majority of which humans cannot see.
　　在日常用语中，＂光＂这个词通常真正意味是可见光 ，这是人眼所感知的类型。 然而，光有许多其他形式，其中绝大多数是人类无法看到的。
　　The source of all light is electromagnetism, the interplay of electric and magnetic fields that permeate space. ​  Light waves  ​ are a form of ​  electromagnetic radiation  ​; the terms are interchangeable. Specifically, electromagnetic waves are self-propagating oscillations in electric and magnetic fields.
　　所有光的来源是电磁力，即渗透空间的电场和磁场的相互作用。 光波是电磁辐射的一种 形式 ； 这些术语可以互换。 具体而言，电磁波是电场和磁场中的自传播振荡。
　　In other words, light is a vibration in an electromagnetic field. It passes through space as a wave.
　　换句话说，光是电磁场中的振动。 它以波的形式穿过空间。
　　Knowledge Points 知识点
　　The speed of light in a vacuum is 3 × 10  ^8 m/s, the fastest speed in the universe!
　　真空中的光速为3×10^8 = m/s，是宇宙中最快的速度！
　　It is a unique and bizarre feature of our existence that nothing travels faster than light. And although all light, whether visible or not, travels at the same speed, when it encounters ​  matter  ​, it slows down. Because light interacts with matter (which doesn＂t exist in a vacuum), the denser the matter, the slower it travels.
　　没有什么比光速传播得更快，这是我们存在的一个独特而奇异的特征。尽管所有的光，无论是否可见，都以相同的速度传播，但当它遇到物质时，它会变慢。因为光与物质（真空中不存在）相互作用，物质越密，传播越慢。
　　Light＂s interactions with matter hint at another of its important characteristics: its particle nature. One of the strangest phenomena in the universe, light is actually two things at once: a wave and a particle. This ​  wave-particle duality  ​ makes studying light somewhat dependent on context.
　　光与物质的相互作用暗示了它的另一个重要特征：它的粒子性质。作为宇宙中最奇怪的现象之一，光实际上同时是两种东西：波和粒子。这种波粒二象性使得研究光在某种程度上取决于上下文的描述。
　　At times, physicists find it most helpful to think of light as a wave, applying to it much of the same mathematics and properties that describe sound waves and other mechanical waves. In other cases, modeling light as a particle is more appropriate, for instance when considering its relationship to atomic energy levels or the path it will take as it reflects off a mirror.
　　有时，物理学家发现将光视为波最有帮助，将描述声波和其他机械波的许多相同数学和属性应用于它。在其他情况下，将光建模为粒子更合适，例如在考虑它与原子能级的关系或它从镜子反射时将采用的路径时。  The Electromagnetic Spectrum 电磁频谱
　　If all light, visible or not, is technically the same thing – electromagnetic radiation – what distinguishes one type from another? Its wave properties.
　　如果所有的光，无论可见与否，在技术上都是同一种东西——电磁辐射——是什么使一种类型与另一种类型区别开来？ 其波的特性。
　　Electromagnetic waves exist in a spectrum of different wavelengths and frequencies. As a wave, light＂s speed follows the wave speed equation, where the speed is equal to the product of wavelength and frequency:
　　电磁波存在于不同波长和频率的频谱中。 作为波，光速遵循波速方程，其中速度等于波长和频率的乘积：
　　V  =  λf
　　In this equation, ​  v  ​ is wave velocity in meters per second (m/s), ​  λ  ​ is wavelength in meters (m) and ​  f  ​ is frequency in hertz (Hz).
　　在此等式中， v 是以米每秒 (m/s) 为单位的波速， λ 是以米 (m) 为单位的波长， f 是以赫兹 (Hz) 为单位的频率。
　　In the case of light, this can be rewritten with the variable ​  c  ​ for the speed of light in a vacuum:
　　在光的情况下，这可以用真空中光速的变量 c 重写：
　　c = λf Knowledge Points 知识点
　　c​ is a special variable representing the speed of light in a vacuum. In other media (materials), light＂s speed can be expressed as a fraction of ​c.​
　　c是代表真空中光速的特殊变量。在其他介质（材料）中，光速可以表示为c的一小部分。
　　This relationship implies that light can have any combination of wavelength or frequency, so long as the values are inversely proportional and their product equals ​c​. In other words, light can have a ​large​ frequency and a ​small​ wavelength, or vice versa.
　　这种关系意味着光可以有任何波长或频率的组合，只要这些值成反比并且它们的乘积等于 c。换句话说，光可以具有大频率和小波长，反之亦然。
　　At different wavelengths and frequencies, light has different properties. So, scientists have pided up the electromagnetic spectrum into segments representing these properties. For example, very high frequencies of electromagnetic radiation, like ultraviolet rays, X-rays or gamma rays, are very energetic – enough to penetrate and harm body tissues. Others, like radio waves, have very low frequencies but high wavelengths, and they pass through bodies unimpeded all the time. (Yes, the radio signal carrying your favorite DJ＂s tracks through the air to your device is a form of electromagnetic radiation – light!)
　　在不同的波长和频率下，光具有不同的特性。因此，科学家们将电磁频谱划分为代表这些特性的部分。例如，非常高频率的电磁辐射，如紫外线、X 射线或伽马射线，非常有能量——足以穿透和伤害身体组织。其他的，比如无线电波，频率很低，但波长很高，它们一直在不受阻碍地穿过身体。 （是的，通过空气将您最喜欢的 DJ 曲目传送到您的设备的无线电信号是一种电磁辐射 - 光！）
　　The forms of electromagnetic radiation from longer wavelengths/lower frequencies/low energy to shorter wavelengths/higher frequencies/high energy are:
　　从较长波长/较低频率/低能量到较短波长/较高频率/高能量的电磁辐射形式是：
　　· Radio waves 无线电波
　　· Microwaves 微波
　　· Infrared waves 红外线
　　· Visible light 可见光
　　· Ultraviolet light 紫外光线
　　· X-rays X射线
　　· Gamma rays 伽马射线The Visible Spectrum 可见光谱
　　The visible light spectrum spans wavelengths from 380-750 nanometers (1 nanometer equals 10-9 meters – one-billionth of a meter, or about the diameter of a hydrogen atom). This part of the electromagnetic spectrum includes all the colors of the rainbow – red, orange, yellow, green, blue, indigo and violet – that are visible to the eye.
　　可见光谱的波长范围为 380-750 纳米（1 纳米等于 10-9 米 ，相当于一米的十亿分之一，或大约为氢原子的直径）。这部分电磁波谱包括肉眼可见的彩虹的所有颜色——红色、橙色、黄色、绿色、蓝色、靛蓝色和紫色。
　　Because red has the longest wavelength of the visible colors, it also has the smallest frequency and thus the lowest energy. The opposite is true for blues and violets. Because the energy of the colors is not the same, neither is their temperature. In fact, the measurement of these temperature differences in visible light led to the discovery of the existence of other light ​invisible​ to humans.
　　由于红色在可见色中波长最长，因此频率也最低，因此能量最低。蓝色和紫罗兰色则相反。因为颜色的能量不一样，它们的温度也不一样。事实上，通过测量可见光中的这些温差，人们发现了人类不可见的其他光的存在。
　　In 1800, Sir Frederick William Herschel devised an experiment to measure the difference in temperatures for different colors of sunlight that he separated using a prism. While he indeed found different temperatures in different color regions, he was surprised to see the hottest temperature of all recorded on the thermometer just beyond the red, where there appeared to be no light at all. This was the first evidence that more light existed than humans could see. He named the light in this region ​infrared​, which translates directly to ＂below red.＂
　　1800年，弗雷德里克·威廉·赫歇尔爵士设计了一项实验来测量他使用棱镜分离的不同颜色阳光的温度差异。虽然他确实在不同的颜色区域发现了不同的温度，但他惊讶地发现温度计上记录的最热温度正好在红色之外，那里似乎根本没有光。这是第一个证明存在比人类所能看到的更多的光的证据。他将这个区域的光命名为 红外线 ，直接翻译为＂低于红色＂。
　　White light, usually what a standards light bulb gives off, is a combination of all the colors. Black, in contrast, is the ​absence​ of any light – not really a color at all!
　　白光，通常是标准灯泡发出的光，是所有颜色的组合。相比之下，黑色是不存在任何光线的——根本就不是一种颜色！Wave Fronts and Rays 波前和射线
　　Optics engineers and scientists consider light in two different ways when determining how it will bounce, combine and focus. Both descriptions are needed to predict the final intensity and location of light as it focuses through lenses or mirrors.
　　光学工程师和科学家在确定光如何反射、组合和聚焦时会以两种不同的方式考虑光。当光通过透镜或镜子聚焦时，需要这两种描述来预测光的最终强度和位置。
　　In one case, opticians look at light as series of ​transverse wave fronts​, which are repeating sinusoidal or S-shaped waves with crests and troughs. This is the ​physical optics​ approach, as it uses the wave nature of light to understand how light interacts with itself and leads to patterns of interference, the same way that waves in water can intensify or cancel one another out.
　　在一种情况下，光学专家将光视为一系列横向波阵面，这些波阵面是具有波峰和波谷的重复正弦波或 S 形波。这是物理光学方法，因为它利用光的波动性来了解光如何与其自身相互作用并导致干涉模式，就像水中的波浪可以增强或相互抵消一样。
　　Physical optics began after 1801 when Thomas Young discovered light＂s wave properties. It helps to explain the workings of such optical instruments as diffraction gratings, which separate the spectrum of light into its component wavelengths, and polarization lenses, which block certain wavelengths.
　　物理光学始于 1801 年，当时 Thomas Young 发现了光的波动特性。它有助于解释诸如衍射光栅和偏振透镜（阻挡某些波长）等光学仪器的工作原理，衍射光栅将光谱分成其组成波长。
　　The other way to think of light is as a ​ray​, a beam following a straight-line path. A ray is drawn as a straight line emanating from a light source and indicating the direction in which light travels. Expressing light as a ray is useful in ​geometric optics​, which relates more to the particle nature of light.
　　另一种将光视为光线的方式，即沿着直线路径的光束。光线被绘制为从光源发出并指示光传播方向的直线。将光表示为光线在几何光学 中很有用，这更多地与光的粒子性质有关。
　　Drawing ray diagrams showing the path of light is critical to designing such light-focusing tools as lenses, prisms, microscopes, telescopes and cameras. Geometric optics has been around for longer than physical optics – by 1600, the era of Sir Isaac Newton, corrective lenses for vision were commonplace.
　　绘制显示光路的射线图对于设计诸如透镜、棱镜、显微镜、望远镜和相机等光聚焦工具至关重要。几何光学比物理光学存在的时间更长——到 1600年，艾萨克·牛顿爵士时代，视力矫正镜片已经司空见惯。