ClassX Video Lessons Youtube Channel SmarterEveryDay What Happens to Lasers Underwater? (Total internal reflection) – Smarter Every Day 219
Hey there! Imagine you’re out on a kayak, just chilling and trying to catch some fish. But when the fish aren’t biting, what do you do? Well, Destin and his friend Trent decided to have some fun with their headlamps underwater. They discovered something super cool: when you shine a light underwater and aim it upwards, the light bounces off the surface of the water. This is because of a phenomenon called Total Internal Reflection.
Have you ever been underwater and looked up to see the sun? You might notice that you can only see the sun from a certain angle. This is called Snell’s Window. It’s like a circular window above you where light comes through, and beyond that, the light reflects away. This happens because of the way light bends when it moves between different materials, like water and air.
Destin and Trent decided to take things up a notch by using lasers. They wore special laser goggles to protect their eyes and used a green laser to explore Total Internal Reflection. When they shone the laser into a block of acrylic at different angles, they saw the light bouncing around inside the block. This happens because the light hits the inside surface at an angle that keeps it bouncing inside, rather than escaping out.
Fiber optics work on the same principle. Light enters the fiber and bounces around inside, traveling all the way through. Destin demonstrated this with a flashlight and fiber optics on his kayak. He even brought a large acrylic rod, which acted like a giant fiber optic, showing how light can travel through it by bouncing internally.
Next, they used a Christmas ornament filled with water to see how light behaves. By changing the angle of the laser inside the ornament, they observed how light bounced around, creating interesting patterns. This showed how Total Internal Reflection can create cool effects when light interacts with curved surfaces.
Total Internal Reflection is not just a fun experiment; it’s a key concept in many technologies. It’s used in fiber optic cables for fast internet, in medical devices, and even in creating beautiful light displays. Understanding how light behaves when it hits different surfaces helps us design better tools and technologies.
Destin also shared a book recommendation, “Just Mercy” by Bryan Stevenson, which made him think about his role in society. It’s a powerful story about justice and helping those without a voice. Just like learning about light, it’s important to reflect on how we can make a positive impact in the world.
So, next time you’re near water or playing with a flashlight, remember how light can bounce and reflect in fascinating ways. It’s all about exploring and getting smarter every day. Thanks for joining this adventure on the river with lasers and learning about Total Internal Reflection!
Gather a clear container, a flashlight, and some water. Fill the container with water and shine the flashlight from below at different angles. Observe how the light behaves as it hits the surface of the water. Try to identify Snell’s Window and discuss your observations with a classmate.
Use a plastic bottle and a laser pointer to create a basic fiber optic model. Fill the bottle with water and shine the laser through the side. Watch how the light travels through the water and discuss how this relates to fiber optics technology.
With supervision, use a laser pointer and an acrylic block to explore Total Internal Reflection. Shine the laser at different angles and observe how the light bounces inside the block. Record your findings and explain why the light behaves this way.
Fill a clear Christmas ornament with water and use a laser pointer to explore light patterns. Change the angle of the laser and observe the patterns created inside the ornament. Discuss how the shape of the ornament affects the light’s path.
Research how Total Internal Reflection is used in real-world applications, such as in medical devices or internet cables. Prepare a short presentation to share your findings with the class, highlighting the importance of this phenomenon in technology.
**Sanitized Transcript:**
– Hey, it’s me, Destin. Welcome back to Smarter Every Day. If you can’t tell, I am on a kayak here. A week ago, I uploaded a video to the second channel where we were trying to fish, right Trent?
– [Trent] Yeah.
– Oh, you’re over there.
– [Trent] I’m over here.
– So we were fishing because we had been working hard and just wanted to relax. The fish weren’t biting, so we decided to play with our headlamps in the water. There’s milfoil all in the water here, and we discovered something really fun with our headlamps underwater. I’ll let you watch a little bit of that video.
– [Destin] Okay, you ready to show them? Get your flashlight and go to the other side. So we figured this out. Put your light in the water, and you can see the beam, right? Now stick your arm further underwater and aim up; it bounces off the top of the water. How cool is that? Neat. If you go too far, it’ll break through. There’s a phenomenon called Snell’s window. You know about Snell’s window?
– [Trent] No.
– If you’re scuba diving, for example, and you’re in the water looking up, you can see the sun, but only from a certain angle. There’s this window right above you where you can see the light coming through; beyond that, the light reflects out. So what Trent is doing over there has to do with the index of refraction of water. Can I try it?
– [Trent] Yeah.
– [Destin] Here, trade the lights with me. Here’s the camera.
– [Trent] Oh, dude, that looks great from over here.
– [Destin] Isn’t that neat? Look at that. You can see the beam going through.
– [Trent] Dude, it bends more with the– Did you see what happens? Half the beam punches through the water, and half the beam doesn’t. Watch, as it comes up, it starts to go dark, and then the whole thing punches through.
– [Trent] Whoa.
– Okay, fast forward to now. We’ve got lasers because some people said in the comments that it would be really cool to do this with lasers. Do you have those laser goggles? I gotta say, this is the only time I’ve ever worn laser goggles. We look a bit silly, but here we go. We’ve got a green laser. It’s not waterproof, so I have it in a bag. For a 532 nanometer laser, and I’m wearing 532 nanometer goggles, which means I can’t see this. I can see that it’s green. So what we’re going to do is play with Total Internal Reflection. I have a bunch of goodies in my kayak. Okay, you ready?
– [Trent] You have no idea how goofy you look.
– This makes so much sense—I love it! Alright, first up, I have a sheet of acrylic. It’s moving my kayak because it’s so big. If we shine this laser into the side of this square acrylic block, you can see that if I’m at a 90-degree angle to the block, the laser just goes straight through and bounces off the other side and diffuses a little bit. But what happens if I angle this laser and bounce it? Look at that, the whole block lights up. The reason it lights up is that the angle at the top is acute, and all that light bounces around inside. This works so much better than I thought it would.
– Alright, so if we go down—let’s go down and see if we can light this block up. Let’s do it. Boom, we hit the corner. Look at that; stuff starts bouncing around. So this Total Internal Reflection is a thing. If we just go straight across, some stays in, some stays out, but—oh, look at that! What just happened? Oh my gosh, I’m bouncing it back and forth. Did you see that?
– [Trent] I can see it with my goggles over here.
– You can see it with your goggles? Okay, here we’re going to do it this way. Boom, right there. You see it bouncing back and forth? Can you see it? Can you zoom in?
– [Trent] It’s really hard to see it on camera.
– Is it really? How do you know? You have laser goggles on, dude.
– [Trent] I can see through the viewfinder.
– So long story short, if you can bounce a laser underneath the angle of incidence, then you can get what’s called Total Internal Reflection. This happens when you have two transparent materials, like air and water or acrylic and air or acrylic and water. Okay, so that’s acrylic. Let’s move on to the next thing. Do we have the fiber optics?
– [Trent] Yes, we do.
– Let’s get the fiber optics on the kayak. Okay, Total Internal Reflection—you totally know what’s up with that. So we have a flashlight and fiber optics. I can’t believe we have all this stuff on the kayaks. So you know how that works, right? The light goes into the fibers and bounces around on the inside, going all the way through. You know what’s about to happen. Where’s my laser?
– [Trent] Oh shoot!
– Alright, here we go. Laser, look at that. Same thing, except I can’t see it because I have laser goggles on. But as I move around, I’m assuming that it’s going through the fibers all the way to the end. The reason it’s able to do that is that it’s bouncing all the way down the fibers like a pipe. Total Internal Reflection. This is all stuff you know; this isn’t new. We’re just demonstrating that because it’s awesome.
– What happens if I shine these fiber-optic lasers into the water? Oh, it kind of looks like a laser flashlight inside that. Okay, alright, so now the way that fiber optics work is really interesting. I happen to bring a bigger version of this fiber optic with me. This is a large dowel of acrylic because obviously, this is what you take on a kayak.
– So the way this works—I’m going to cut this off. This is going to look like a lightsaber. Are you ready for this? Ready, one, two—whoa.
– [Trent] Put your goggles on.
– Oh yeah, my goggles. Thank you. Oh man, does it look awesome?
– [Trent] It does look amazing.
– Okay, can you see through?
– [Trent] I can only see it through the camera.
– Yeah, because we’re being safe.
– [Trent] It looks incredible.
– Okay, so the reason this looks like a gigantic fiber optic is that it is. You can tell that it’s an optic because of the way it is. Alright, so you’ve got this low angle of incidence here; it’s amazing.
– [Trent] Put it in the water.
– Can I light up the whole water? I can’t see that. Is it lighting up the water?
– [Trent] We’re about to look.
– Is it lighting up the water? It’s like a big flashlight at the end. I don’t care; I’m going to quit talking and just do stuff. You could make a camera that would see all the way to the bottom, couldn’t you? It’s a light pipe.
– [Trent] A light pipe.
– You could totally see if it was polished on both ends; you could make a camera that could go all the way to the bottom. Alright, we brought a gigantic piece of acrylic on a kayak. So we’ve done the square acrylic. We’ve done the fiber optic, both small and large. It’s time for the Christmas ornament.
– Okay, we have a Christmas ornament, and we’ve got murky water below. We’re going to need goggles for this one. Oh, we got some milfoil in there. That’s going to make it more interesting. Just people on boats with lasers—that’s all this is. Alright, so here we go. We should be able to see the light go straight through. I can barely see it, but what should happen is if I change the angle inside, we should get some weird bouncing going on, right?
– Yeah, we do. Let’s get up here close. So we’re firing straight inside right there, and if I start to bounce things off the inside by shooting it across the cord instead of the diameter, we get all kinds of weirdness. What would be really cool is if we could take a shadowgraph of this; if we could blast this onto a large wall, we would see all the microbes and little things living inside there.
– Internal Reflection does not have to be total. If you meet this interface between the glass and the air, for example, some of the light goes out, and some of the light stays in, and that’s why Total Internal Reflection is so cool. Oh, look at that! When I hit that seam, you see that? When I hit the meniscus at the top where it curves, it just lights up the whole bulb. You see what I’m saying? It makes a huge globe.
– So boom, I hit the curve, lights up straight across, doesn’t light up. That’s fun; we’re having fun. We’re learning things on kayaks with lasers. Okay, so now it’s time for more good sounds. I think it’s time.
– [Trent] It’s time.
– Laser underwater. We’re going to see if we can bounce the laser off the bottom of the water. Here’s the Christmas ornament. Everybody knows what’s going to happen. If the angle that hits the top of the water from underwater is less than 50 degrees, then it’ll bounce back into the water. But if it’s above that, it’ll punch out. I just want to see it from underwater.
– Okay, here we go. Tilt it back down at some point; all of the light should bounce underwater. You should see the beam get lighter and lighter as I point up more that reflected beam. So as it’s laying down, you should see a full laser beam in the water. As I tilt it up and it bounces off the top, that reflected beam should get lighter and lighter as I go up, and then at the maximum angle, once it hits the critical angle, the one inside should go dark, and all the light should come straight out, which is completely rad.
– In this video, we talked about the ability of light to bounce on the inside of an object in a certain way called Total Internal Reflection. I would like to tell you about a book that made me reflect internally as well; it’s called “Just Mercy” by Bryan Stevenson. This episode of Smarter Every Day is sponsored by Audible, and I really want you to read this book. Bryan Stevenson is the lawyer for Anthony Ray Hinton, who was wrongly convicted of murder in Alabama and sentenced to death row. Bryan Stevenson came to his aid and helped Anthony Ray Hinton get out of death row. It’s an amazing book. I loved it. It made me reflect on my role in society and how I could help those without a voice.
– So please go check this out by going to Audible.com/Smarter or texting the word “smarter” to 500-500. The first book is free. You can get two free Audible originals. This is a big book for me in terms of making me think about my place in the world and what kinds of things I could do to help others. So again, you can get a free book or a free 30-day trial in Audible by going to Audible.com/Smarter or texting the word “smarter” to 500-500. I highly recommend this book; you will totally dig it.
– So anyway, thank you for enjoying Total Internal Reflection time with me here on the river. That’s amazing. That’s really cool stuff, so I hope you enjoyed that. Last thing, feel free to unsubscribe from Smarter Every Day if you feel like this video earned it. By unsubscribe, I mean you could unsubscribe and then resubscribe if it earned it. And then click the bell to turn notifications on. If not, that’s no big deal, but I hope you enjoyed this. I mean, playing with Total Internal Reflections on a kayak is just absolutely awesome, so I hope you enjoyed this half as much as I do. I’m Destin; again, feel free to subscribe. Getting smarter every day. Have a good one, bye.
Lasers – Devices that emit a concentrated beam of light through the process of optical amplification based on the stimulated emission of electromagnetic radiation. – Scientists use lasers to measure distances with high precision.
Light – A form of energy that travels in waves and can be seen by the human eye. – Light travels faster than sound, which is why we see lightning before we hear thunder.
Reflection – The bouncing back of light rays when they hit a surface that they cannot pass through. – The reflection of light off a mirror allows us to see our image.
Total – In physics, often refers to the complete amount or sum of a particular quantity. – The total energy of a system is conserved, meaning it remains constant over time.
Internal – Located or occurring within a particular medium or object. – The internal energy of a gas increases when it is heated.
Snell’s – Referring to Snell’s Law, which describes how light bends when it passes from one medium to another. – Snell’s Law helps us understand how lenses focus light.
Optics – The branch of physics that deals with the study of light and its interactions with different materials. – Optics is crucial for designing instruments like telescopes and microscopes.
Acrylic – A type of plastic material that is often used in lenses and other optical devices due to its clarity and light weight. – Acrylic lenses are used in some eyeglasses because they are lightweight and durable.
Angle – The space between two intersecting lines or surfaces at or close to the point where they meet. – The angle of incidence is equal to the angle of reflection when light bounces off a flat surface.
Water – A transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth’s streams, lakes, and oceans. – Light slows down when it enters water from air, causing it to bend.
