82 Light-Mid

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 important 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。 但让我们看到东西只是光的一个重要方面，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 kind of energy. called radiant energy But the light you can see is only one kind and a very small part of radiant energy. There are many kinds of radiant energy, and scientists usually describe the whole range as a spectrum—a series of energy bands. The diagram above shows the major bands of radiant energy. Visible light is only a small part of the spectrum, in the middle. On each side of visible light is invisible radiant energy. The bands on the left of the diagram have less energy than the bands on the right. For example, radio waves are much less powerful than gamma waves. You can see bands of color in a rainbow. Each of these bands is made by radiant energy with a different amount of energy than the band next to it.

光是什么?光是一种能量。 但是你看到的光只是辐射能的一种，而且是辐射能的很小一部分。 辐射能有很多种，科学家通常把整个范围描述为光谱——一系列的能带。 上图显示了辐射能的主要波段。 可见光只是光谱的一小部分，在中间。 在可见光的两侧是不可见的辐射能。 图左边的能带比右边的能带能量少。 例如，无线电波比伽马波弱得多。 你可以在彩虹中看到色带。 每一个波段都是由辐射能构成的辐射能与它旁边的波段的能量不同。

How Light Moves Scientists describe light and how it moves in two ways. The first way is as tiny, invisible packets of energy called photons. Photons are particles of energy. They don't weigh anything, even when billions get together! Not all photons are equal. High-powered gamma rays have photons with more energy than photons of visible light. Even in visible light, there is a difference in energy from one color to another. For example, violet light photons carry more energy than red light photons.

科学家们用两种方式来描述光及其运动方式。 第一种方法是微小的、看不见的能量包，称为光子。 光子是能量的粒子。 即使数十亿人聚在一起，他们也没有任何重量!不是所有的光子都是相等的。 高能伽马射线的光子比可见光的光子能量更大。 即使在可见光中，一种颜色与另一种颜色的能量也有差异。 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 by their frequency, or how closely together they travel. High-frequency waves, travel more closely than low-frequency waves which are more spread out. More high- frequency waves pass a given point in a period of time than low-frequency waves. Scientists measure frequency by a wave's 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 wave is more spread out. It has a longer wavelength. The longer the wavelength, the lower the wave's energy.

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

There are several more things to know about how light moves. One is that it travels in straight lines. Another is that beams, or rays, of light can change direction. We will read more about this in the section on how light behaves. A third important thing to know about how light moves is that—unlike sound—it does not need a medium such as air, water, or wood to travel through. This makes radiant energy special—it can travel through the emptiness of space. If radiant energy could not do this, sunlight would never reach Earth.

关于光的运动，还有几件事需要了解。 一是它沿直线传播。 另一个原因是光束或光线可以改变方向。 我们将在光的行为一节中阅读更多关于这方面的内容。 关于光的运动，我们需要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。 这使得辐射能很特别——它可以穿越虚空的空间。 如果辐射能不能做到这一点，阳光就永远不会到达地球。