83 Light-High

Light Written by Brian Roberts

布莱恩·罗伯茨(Brian Roberts

Introduction If you've ever walked into a closet and closed the door, you've experienced a world without light. Without light, we can't see a thing. But allowing us to see things is only one aspect of light, especially sunlight. This book will reveal many of the fascinating facts that scientists have discovered about light. These facts include what it is, where it comes from, how it moves, and what happens when light strikes different surfaces. There is much more to light than meets the eye.

如果你曾经走进一个壁橱，关上门，你就经历了一个没有光的世界。 没有光，我们什么也看不见。 但是让我们看到东西只是光的一个方面，尤其是阳光。 这本书将揭示许多科学家们已经发现的关于光的迷人事实。 这些事实包括它是什么，它从哪里来，它如何移动，以及当光照射到不同的表面时会发生什么。 光比眼睛看到的要多得多。

What Is Light? Light is a form of energy called radiant energy. But the light you can see is only one kind of radiant energy. Scientists usually describe the range of radiant energy as a spectrum, or a series of energy bands. The diagram above shows all the major bands of radiant energy. Visible light bands are in the middle of this spectrum but are only a small part of it. On each side of visible light are bands representing invisible radiant energy. Those on the left side have less energy than the bands on the right side. For example, gamma rays are much more powerful than radio waves. Sunlight is actually a mixture of many colors. Light passing through a prism is separated into many bands of color— the same colors seen in a rainbow.

光是什么?光是能量的一种形式，称为辐射能。 但是你所看到的光只是辐射能的一种。 科学家通常把辐射能的范围描述为光谱，或一系列的能带。 上图显示了辐射能的所有主要波段。 可见光波段位于这个光谱的中间，但只是其中的一小部分。 在可见光的两侧是代表不可见辐射能的条带。 左边的能带比右边的能带能量少。 例如，伽马射线比无线电波强大得多。 阳光实际上是多种颜色的混合物。 穿过棱镜的光被分成许多色带——和彩虹中看到的颜色一样。

How Light Moves Scientists have two ways to describe light and how it moves. The first way describes light as tiny, invisible particles, or packets, of energy called photons. Because photons are energy, not matter, they have no weight— even if you gather together billions of them! Not all photons are equal. High-powered radiant energy, such as gamma rays, has photons that carry more energy than photons of visible light. Even in visible light, one color of light might have more energy than another. For example, violet light photons carry more energy than red light photons.

光如何运动科学家们有两种方法来描述光及其运动方式。 第一种方法将光描述为微小的、看不见的粒子，或称为光子的能量包。 因为光子是能量，而不是物质，它们没有重量——即使你把数十亿个光子聚集在一起!不是所有的光子都是相等的。 高能辐射能，如伽马射线，其光子比可见光的光子携带更多的能量。 即使在可见光中，一种颜色的光也可能比另一种颜色的光具有更多的能量。 例如，紫光光子比红光光子携带更多的能量。

Light is also described as moving in waves. These waves are measured in terms of their frequency, or how closely together they travel. High-frequency waves travel more closely together, meaning that more of them pass a given point in a period of time than low-frequency waves, which are more spread out. Scientists measure frequency by a property called wavelength. Wavelength is the distance between the peak of one wave and the peak of the wave next to it. Look at the diagram of a high-frequency wave and a low-frequency wave. The low-frequency waves are more spread out— they have a longer wavelength. The longer the wavelength, the lower the wave's energy.

光也被描述为波状运动。 这些波是根据它们的频率或它们传播的紧密程度来测量的。 高频波传播的距离更近，这意味着在一段时间内通过给定点的高频波比低频波更分散。 科学家通过波长来测量频率。 波长是一个波的峰值和它旁边的波的峰值之间的距离。 看一下高频波和低频波的图。 低频波更分散，波长更长。 波长越长，波的能量越低。

There are several things you should know about the movement of light. One is that it travels in a straight line. A second is that beams, or rays, of light can change direction. You will read more about this in the section on how light behaves. A third important thing you should know about light's movement is that, unlike sound, it does not need a medium such as air, water, or wood to travel through. This is what makes radiant energy so special— it can travel through the nothingness of space. If it were not for this special property of radiant energy, sunlight would never reach Earth.

关于光的运动，有几件事你应该知道。 一是它沿直线运动。 第二个原因是光束或光线可以改变方向。 你将在光的行为部分读到更多关于这方面的内容。 关于光的运动，你应该知道的第三件重要的事情是，与声音不同，光不需要空气、水或木头这样的介质来传播。 这就是为什么辐射能如此特别——它可以在虚无的空间中传播。 如果不是因为辐射能的这种特殊性质，阳光就永远无法到达地球。