81 Light-Low

LIGHT Written by Brian Roberts

布莱恩·罗伯茨著

Introduction If you've ever walked into a closet and closed the door, you've been in a world without light. Without light, we can't see. But allowing us to see things is only one important thing about light. This book will reveal many of the fascinating facts that scientists have found out 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，你就进入了一个没有光的世界。 没有光，我们就看不见。 但让我们看到事物只是光的一个重要方面。 这本书将揭示许多科学家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. It is called radiant energy. There are many kinds of radiant energy, but light is the kind you can see. Scientists usually describe the range of energy as a spectrum. A spectrum is a series of energy bands. The diagram above shows 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 have less energy than the bands on the right. For example, radio waves are much less powerful than gamma waves.

光是什么?光是一种能量。 它被称为辐射能。 辐射能有很多种，但光是你能看到的那种。 科学家通常把能量的范围描述为光谱。 光谱是一系列的能带。 上图显示了辐射能的波段。 可见光只是光谱的一小部分，在可见光的两侧是不可见的辐射能。 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。

How Light Moves There are two ways to describe light and how it moves. The first way is as tiny, invisible packets of energy called photons. They don't weigh anything—even billions of them together! Photons have different amounts of energy. High-powered gamma ray photons have more energy than photons of visible light. Even in visible light different colors of light, have different amounts of energy. For example, violet light photons have more energy than red light photons.

有两种方法来描述光和它如何移动。 第一种方法是微小的、看不见的能量包，称为光子。 它们没有任何重量——甚至是数十亿个加在一起!光子有不同的能量。 高能伽马射线光子比可见光光子有更多的能量。 即使在可见光中，不同颜色的光，也有不同的能量。 例如，紫光光子比红光光子有更多的能量。

The second way of describing light is as a wave. Waves are measured by their frequency, or how closely together they move. High-frequency waves travel more closely together. Low-frequency waves are spread out. More high-frequency waves than low-frequency waves will pass the same place in the same time. 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 two waves. The low-frequency wave is spread out. It has a longer wavelength. The longer the wavelength, the lower the wave's energy.

第二种描述光的方式是波。 波是由它们的频率或它们移动的紧密程度来测量的。 高频波的传播距离更近。 低频波被扩散。 在同一时间内经过同一地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。 看这两个波的图。 低频波被扩散开来。 它有更长的波长。 波长越长，波的能量越低。

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

关于光的运动，还有一些事情需要了解。 一是它沿直线传播。 另一个原因是光束可以改变方向。 你将在光的行为部分读到更多关于这方面的内容。 关于光如何移动，我们需要知道的第三件事是，与声音不同，光不需要通过任何东西，比如空气、水或木头。 这使得辐射能很特别——它甚至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。