ChapterOnLight - Chapter 5 Light and Doppler Shifts A large...

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5 - 2 Chapter 5 Light and Doppler Shifts A large amount of what we have learned in science comes from what we see when we “look” at things. The act of looking, for most living species, is what occurs when light coming from something hits our eyes. We know the Sun exists because we see the light coming from it. We see the walls in a room around us because light bounces off them and into our eyes. Similarly, we know about atoms because of the light we see that is emitted from them, or bounces off them. There is a lot more to light than meets the eye. For example, there are many different kinds: some that we can see with our naked eyes, others that we cannot. Many people know the phrase “at the speed of light” and recognize that it is a really fast speed. To truly understand light, though, you must first realize that it acts as both a wave and a particle. Since most people do not typically think about light in this way, we will start by talking a bit about what it means to be “wave-like” and “particle-like.” After that, we will discuss the different things we can learn from each. For example, since light behaves like a wave, it can undergo what scientists call the Doppler effect . By understanding and utilizing this phenomenon, we can figure out whether a star or galaxy is moving toward us or away from us. Using properties of both particles and waves have allowed scientists to conduct better experiments and gather more clues about the universe. It is remarkable how much we can learn about the little white dots in the sky by looking at the light that comes from them.
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5 - 3 5.1 Light as a wave Since the light we see with our eyes acts like a wave, it is important to understand what we mean by “wave.” Most people have been to the beach and seen waves as they come into the shore (see Figure 5.1). It is not hard to see the peaks (where the water is above usual height of the water level) and troughs (where it is below). When scientists talk about waves, they do not talk about the individual wave that crashes on the beach, but rather the amount of space in between the corresponding parts of the waves; for example, between the peaks of two neighboring waves. This distance is known as the wavelength . <FIGURE 5.1 ABOUT HERE> How do we know that light is a wave? In order to answer that question, we start by explaining one of the important properties of waves. Imagine you are sitting at the beach, but this time, the waves are crashing directly into a wall. You will not see any waves on the other side of the wall because the waves cannot travel through it. However, the situation can be very different if there is a single small hole in the wall. As the waves roll in, the water pushes through the hole and produces waves on the other side. If you look at these waves, they will no longer be straight lines, but rather semi-circles—like half of the circle you would see if you dropped a rock in a puddle of water.
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  • Spring '14
  • Dr.JonathanAsaadi
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