Wave transmission | Waves | Middle school physics | Khan Academy

When we're talking about waves, transmission is when a wave passes from a material into another one. For example, here we have the sun, 93 million miles away on average, and imagine the different materials that the light has to travel through from the sun to say hit one of these sand particles right over here.

Think about what it needs to be transmitted through. Well, it's going to travel through 93 million miles of the vacuum of space, and that's one of the amazing things about light waves is that they don't need a medium; they can travel through vacuum, through emptiness. But then, it's going to travel through several miles of Earth's atmosphere, so it's going to travel through several miles of Earth's atmosphere.

It'll hit these lenses of these sunglasses; it'll actually travel through the lenses of the sunglasses. The sunglass has some width or some depth to it, and then it'll go out onto the other side, and it will hit the sand right over here.

Now, one thing you might realize is the amount of transmission and what gets transmitted is dependent on the wavelengths of the wave, in this case, the wavelengths of light, and also about the material that they are going through.

So, for example, these sunglasses right over here, many sunglasses try to keep out UV light (ultraviolet light), which is a higher frequency than visible light. But that's what causes sunburns, and that can also damage your eyes, so those high frequencies are not making it through.

We could also see that this sunglass right over here kind of has an orangish color, which means that things that are closer to that end of the spectrum, closer to the red, the oranges, and the yellows, are getting through, which means that it's filtering out blue light.

So the blue light isn't getting transmitted through as much as, say, the red, orange, and yellow light, and that's why we see this as red, orange, or yellow. And then, of course, the light will get to that sand particle.

Now, transmission, as I mentioned, isn't just about light waves. We could talk about one of our other favorite types of waves; for example, sound waves. If you are in a room, you have probably experienced the fact that even if you were to close the door—and I do this a lot because I record a lot of videos—this is me in my little closet recording a video.

This is a top view of what I'm doing right now. A lot of times, my kids are in other parts of the house, and they're making a lot of noise. As we've talked about, sound waves are nothing but traveling pressure waves through the air. Those air particles are knocking one into another, but in order to make it to me, they need to get through that wall.

The way they do that is they get transmitted through that wall, so those air particles make the particles—or make the atoms or the molecules—in the wall start vibrating. They bump into each other, and then the particles on the other side of the wall will bump into the air in my little closet, and then we will have, once again, the sound waves make it to me.

Now, the overall magnitude of the sound, the volume of the sound, will likely be diminished, and not all of the frequencies of the sound will be transmitted equally. Different frequencies of sound waves are better at traveling through certain materials, just as we talked about with light waves.

So now, when you look at the world around you, or you hear the world around you, or look at other types of waves, just think about how it's transmitting from one material into another.