On Super Tuesday today, we're going to make a giant magnifying glass, a huge lens to melt things that can reach almost 700 degrees Celsius. For a change, this is an experience that is cool to see in the video, but not to do at home. Although this material that we are going to use, you will see that it is not at all easy to find.
You must have already played with a magnifying glass like this one to burn something in the sun, we even lit a fire in Manual do Mundo using a magnifying glass. When I was a kid, I played killing ants with a magnifying glass. Don't do this at home.
Let's quickly understand how it works. Imagine that the sun's rays are alive from here to here. They arrive more or less parallel, all side by side, very straight.
After they pass through the lens, the lens deflects these light rays. So look how cool. The light ray is coming straight, and the lens deviates.
Just look at one thing. As I move around here, you can see that the offset is different. So if you have a bunch of parallel rays arriving at the lens, they all end up going to one point.
That's why this one here is a converging lens, because it makes light rays converge. If I put my hand here, you can see that the light is practically at the same point there. That's the focus point, that's the point where this magnifying glass is going to burn something because it's concentrating all the light there.
And the cool thing is that it also happens the other way around. I'm going to place a flashlight exactly at the focus point, where the light was focusing. Look how crazy.
Now the light leaves here, it leaves opening, when it reaches the lens it stops opening and continues in a straight line. It forms a kind of a cannon of light. I'm going to put a little more smoke so you can see it more clearly.
Of course, light cannons are really cool things for us to see, but they also have a very cool practical function, which is to be used in those lighthouses that are on the edge of the sea so that ships can guide themselves. So, in the 1800s, lighthouses already existed, but they had a very serious problem. They could not make this beam of light for the next one, in the lighthouse they needed a very large lens to be able to make the beam.
And a very large glass lens is impossible to make, because it would be extremely heavy, you would need a crane that did not exist at that time. No one would be able to carry it, it would be very expensive and, one more thing, if you have too much glass, light has a little difficulty passing through the glass. So, the glass would end up taking away some of the light effect.
Who ended up solving this problem was a Frenchman named Augustin Jean Fresnel. He decided to remove a piece of the lens to save glass, it's much lighter and look at the idea the guy had. Imagine that this is the lens that Augustin Jean Fresnel wants to put on his lighthouse.
It is logical that this glass here would already weigh about 300 kilos. In the lighthouse it is even bigger. And then he decided to prick the lens as follows.
First, he divided the lens into several parts. I'm doing a simulation here, so it's not exactly what Fresnel did, but let's assume this is it. And then he decided to cut some parts out.
The guy simply discarded all of this here. Everything I'm scratching here, he threw it away and then cut the glass like this. This little piece here.
Look how crazy, this looks like a saw, but no. This right here is a lens that works identically to how it worked before cropping. But now it's much lighter, it doesn't have all that amount of glass here and it's much easier to produce and after putting it up there in the lighthouse for the ships to see.
As soon as Fresnel put this over there in his lighthouse, he started to be seen from 30 kilometers away. The ship that was 30 kilometers from the lighthouse could see the lighthouse and this was previously impossible because the light was dispersed and now the light will retain it without dispersing. It is still widely used today, whether in traffic light, in airport approach light, in any type of light cannon, whether for theater lighting, cinema lighting, nightclub lighting, those that face upwards.
He also uses it in front of those giant televisions like the one I took apart with Luciano Amaral. By the way, yes, we kept it since we disassembled the television to do this experiment. So I'm going to start by extracting the lens from this pile of junk here that was used to protect it.
Here it is! It smells like pee, what a weird thing. Now, you realize that we have a problem here, right?
The lens is soft, it is completely flexible, so there is no way for a person to keep holding this lens in the right position while adjusting it in relation to the incoming sun rays. We need a nice support to hold. First of all, I'm going to make a kind of frame similar to the one that was already on television, only much more reinforced.
Similar to a picture frame. To attach the lens on top of this rectangle, I'm going to make some holes in the plastic and put a screw with a washer. Now, the thing is clean, it's robust and I need to make a lateral support for this thing to stand up on its own.
We've already done some tests here and found out that the ideal height is around one meter and 80 centimeters. I'm going to cut the legs one meter high and then we'll adjust the object that's going to be burned. As I have this super saw here, I'm going to take the opportunity to make a little more neat foot to practice some woodworking skills here from Manual do Mundo.
Here's an optical instrument capable of making our little friend Augustin Jean Fresnel jealous, huh? Doing a test, we see that the focus of the lens is more or less 86 centimeters from it. Stopped, stopped, stopped.
Wait. Before we put things out in the sun, let's just do a really cool experiment that I've always wanted to do. Let's see if this fresnel lens really works right, if it actually makes light rays converge to the same point.
I'm going to put a parallel light here and see the little funnel forming up ahead. Imagine that this one here is the ray of sunshine. All the parallel rays arrive there and, on the other side, they all have to go to the same point, they have to cross there at the focus point.
So, I'm not seeing the other side. Now it should be facing downwards, now it should be almost straight and now facing upwards. Right?
Is that what you're seeing there? If so, we have a fresnel lens. As we don't have a collection of lasers here, we'll take a long exposure photograph, it's catching the light for a long time, then you'll be able to see the light converging perfectly, and we'll find that point of focus perfectly .
Just look! On the left side there would be the sun entering the lens, and on the right side you can see that it concentrates on a point, concentrates on the focus. And then it will get very hot.
I think that just for these light simulations on the laser, I think it was worth a thumbs up, huh? Just look! It's 10 am, the weather forecast is sunny with absolutely no clouds.
It's the right day for us to test this here. Positioning it is very easy, because I did my best with the carpentry, so everything is in line. First thing is to align this part here in relation to the sun.
I make the shadow of this coincide on top of this here. I know that in that direction, it's aligned. The secret is here.
This part is in the sun, I keep turning, turning, turning until one hour the shadow arrives. So, at this point, at this threshold between Sun and shadow, I know that it is exactly, here it is exactly in the same direction as the Sun. And here it is 90 degrees relative to the sun's rays.
And the last test is finding the point of focus, is knowing where the light rays are meeting. The way you just saw, there's no way. You have to take a piece of wood and hunt for the focus point, you will see that it is very easy to find.
And I'm using these glasses here, which are the welding glasses, they are made so you can look at the absurd light that will appear here. We will see. Pay close attention.
Look, here it's out of focus, I'm going down, I know the focus point is further down. I found the focus point. Dude, I'm going to record it up close so you can see.
Look how long it takes for this wood to catch fire. Let's start with the most useful thing we could do with this lens. .
. Which is to pop a popcorn. Just standing the frying pan in the sun, it's already warm, the margarine is already starting to melt on top of it.
But you can see that it is not hot, otherwise the margarine would disappear. I'm going to mix the popcorn corn well, I think it's worth putting a little more to increase the chances of success. We have popcorn here.
A little popcorn popped, but we realized it was burning the corn. I moved the corn away from the focus position to heat the pan first and then pop the popcorn. The next time you go to the movies, just make a fresnel lens and put it in the sun first.
You will get free popcorn. Or almost. The next step is a classic of Brazilian cuisine, bread with fried egg.
Let's first toast the bread, a little oil. . .
Bread with egg fried in fresnel lens, a rare experience in your life. Is perfect. You know if I try to put a thermometer down there or measure the temperature with my infrared thermometer or infrared camera it won't work.
These thermometers reach 300 degrees Celsius, and I think this goes way beyond that. We made a little table with things that we are going to try to melt there, so it starts with sulfur, at 115 degrees, and goes to glass, which melts at 1250 degrees. Place your bets below.
What do you think will melt? How far will our super lens go? I'm going to start by testing with a small piece of cork just to see if the focus is right.
We painted everything black because it will absorb a lot more light and it will heat up more easily. If not, it starts to reflect the sun and then it doesn't work right. So, we always leave a strip unpainted to know what material it is.
Let's see if the cork catches fire easily and if the focus is right. This one is cork. I think our setup here is fine.
This white brick that you can see below, this piece here is a refractory brick, this is used inside barbecues, inside fireplaces. The advantage of it is that it does not break. You can put it at a very high temperature and it won't crack.
We've tried several things down here, tiles, a lot of things, everything cracks. Burnt cork smell. It looks like a June party.
Sulfur melts at 115 degrees. We put it here in a can with a black background, let's see what will happen. Are you able to see?
Not only did it melt, it started to burn and the smell of that stuff is hellish. Let's then go to lead alloy with tin. This alloy here is used in soldering, soldering electronics.
Its melting point is 183 degrees. If this thing melts, that means the lens has reached 183 degrees. It melted, like, in a second!
Bismuth I'm even sorry to melt. 271 degrees Celsius to enter liquid state. This thing is so beautiful when it crystallizes that.
. . let's do this.
In the name of Science! That's bismuth. The bismuth turned into a puddle of molten metal.
Lead. 327 degrees celsius. Look what's left of it here.
This right here is a piece of a soda can. Aluminum. 660 degrees Celsius.
Aluminum! That smoke, at first, is from the paint, it's not that the aluminum is melting, no. Pierced the aluminum plate.
It punctured aluminum very easily, and the problem is that we don't have anything very close to aluminum to test afterwards. We have to go straight to copper, which is 1,085 degrees Celsius. No sign of melting.
Let's try it with glass that's over 1,200 degrees Celsius. Just for conscience sake. And since now it's a much bigger challenge, we protected a little from the wind and placed a brick that was painted black under the place where the fire will burn.
This way it will absorb much more heat. Let's go! It has a face that looks like it's going to melt.
. . funny that it casts a shadow around the lens.
I'm going to take a brick here for the top of the lamp to be in the focus of the lens. The whole lamp doesn't look like it's going to work, no. Let's try to break the glass to get it exactly in focus.
The lamp is not wanting to melt. I did some research and saw that the lamp's glass could be much more resistant, because it has to stay at a very high temperature. It may be borosilicate glass, for example, which will take much longer to melt and is much more resistant.
So let's try it with more common glass, a beer bottle, and see what happens. It takes time to distribute the heat in it. But it was about to burst, right?
At least we know that the bottle pops well. Let's fix the glass up here again. Oh no!
Don't burn my box! Yeah, guys, I think we found the limit of our fresnel lens here. It spent about 20 minutes scorching in the sun, no sign of melting and now the weather has clouded over, the sun is gone.
And we discovered that the maximum temperature of this thing today is around 700 degrees Celsius. At least now, every time you go fry an egg, make popcorn or look at a lighthouse by the sea, you'll remember this here, okay? Don't forget to subscribe to Manual do Mundo, if you haven't subscribed yet, and give this Super Tuesday a thumbs up, which was pretty cool, right?
