Now, we have talked about particles. What about waves? Before we start talking a
Now, we have talked about particles. What about waves? Before we start talking about waves, it’s probably best to give a few different examples of waves. If I ask you to think of a wave the first thing that probably would come to most your minds is a water wave, but we could also have waves on a string, or even sound waves. The most generic picture that a lot of you have, is probably some sort of sine or cosine shape traveling along, but this is not representative of all waves and we want our definition to be in terms of properties that apply to every possible wave that we can think of.
Let’s go through a few questions and develop a definition of a wave.
Does the wave actually have to go anywhere, does a wave travel? No. Sure, most waves go somewhere, water waves travel across an ocean for example, but think of a guitar string, when you pluck it, certainly the string waves back and forth but the string doesn’t go anywhere, the wave stands on the string. This is called a standing wave. So, traveling cannot be part of our definition of a wave.
Does a wave have to be a repeating pattern? Again, not really. While this might be the image that a lot of you have in mind when I say the word wave, remember we can have just a single pulse going back and forth on a string.
Does the wave have to have up and down motion? Well again, no. The standard picture of a wave that you have in your head might look like Figure 1, but I could also send a compression wave down the slinky like in figure 2 where the links of the slinky move back and forth in the same direction as the waves motion.
Now we need a little bit of terminology. Waves that do wiggle perpendicular to the direction of motion of the wave are called transverse waves. These are the waves that you probably have in mind and these are the ones that were mostly going to be interested in.
The basic terminology of transverse waves, we’ll introduce some more later, are that waves have a peak and a trough, and then the distance from the zero line to either a peak or a trough is called the amplitude. This amplitude is labelled in Figure 3.
Figure 3: Parts of a wave (Credit: Krishnavedala)
What other properties of a wave could we perhaps use? Can a wave bend around corners? We know that particles don’t bend around corners, what about waves? Well, it turns out that waves do bend around corners. Think of a water wave, it spreads out, bending around the corner. In the video on the next slide we’ll see some other important properties of waves that all waves do share.
I go and just hit the water with a single stick, we see we get waves coming out in all directions, radiating away from the spot where the ball hits the water.
Things get a little bit more interesting, however, if we have two sources of waves going at the same time next to each other like so.
So now we get two waves, each radiating out from its source. In some places the waves line up peak to peak, or trough to trough, and add up, resulting in a larger wa