Things You Can Do With A Giant Fresnel Lens

Ant writes "Here is a link where this guy always wanted Edmund Scientific's Giant Fresnel Lens. 'Melts asphalt in seconds!' the ad said. When he went to graduate school he met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began."

EEK!

Lets hope this doesn't get into the wrong hands! This can be worse than WMD's!

Re:EEK!

It already is because this actually exists.

Re:EEK!

I know; I just finished with the AP Physics B test, and I thought I was rid of specific heats forever. Why, God?? Why won't they die?

Burnination

And to think, when I was a kid I had to settle for burning ants with a magnifying glass.

Re:Burnination

Heh! When I was in High-school we took things a step farther by taking Mr. Bouknecht's overhead projector lens out of the housing. [I'm quite certain] it's a true Fresnel Lens - but the point is that it was like a magnifying glass on steroids. We had to be careful just walking out into the parking lot with it because if it caught a friends leg and the sun at the right angle, they'd be in a world of hurt.

Aaahh, fun times being a juvenille. My advice to the next generation though - be as mischievious as normal, but don't do anything stupid or anything that will get you thrown in jail. Be intelligent with your "inevitable" delinquency [you call it rebellion] - we've all been there - however don't get anyone hurt or needlessly damage property.

Life is much more exciting as an experienced adult making thousands of dollars a month. Trust me on this one all you guys. Science is fun, but it can also be very dangerous... Be safe - because if you go to jail or die, the guy you hate will likely reproduce and you never will. And that would suck.

Re:Burnination

Science is fun, but it can also be very dangerous... Be safe

My father once caught me making gunpowder using a chem lab kit he'd bought me and an old mortar I'd found in the garage. His first reaction was "Idiot kid!" Then it was "Oh, wait, that's what I used that mortar for when I was a kid. Let me show you how to do it safely." Basically wet the ingredients down so it doesn't accidentally catch fire while you are grinding it. I suspect he'd learned that one the hard way. I'm big on the safety angle with my kids now, too. In my case its a result of an experiment with some gasoline and an Estes rocket engine when I was a teenager.

Nice picture of a giant fresnel lens in action

Right here: Cooking with Light [armory.com].

Ants

Now the ants really don't stand a chance!!!

Re:Ants

Even ants the size of horses.

Re:Ants

DOH! :(

Avoid antabuse at all costs

A buddy who was in the army was busted for showing up drunk, and they made him take antabuse [wisc.edu]. According to him, when you're taking it drinking even the smallest amount of alcohol makes you puke puke puke.

Re:Ants

Ants? I'm more worried about the humans [channel4.co.uk].

Ideas

Mount it in front of your monitor for a really big image Write your name in the side of someone's car Wipe your harddrive permanently There has to be a way to increase solar cell output with these (not at direct focus of course mabey larger area at 25% focus)

It's being done!

that's actually how some solar power stations work. They have a bunch of mirrors that aim the sunlight to a glass globe filled with water, the water boils out and powers a turbine, condenses out and returns to the globe via a valve and pump.

Overall it works better than solar cells because it's so simple and you harness the heat energy rather than the light itself, but therer's only economy to it on a large scale, you need enough space to get a huge amount of water to constantly boil. Also, it's significantly harder to get this thing working on less-than-ideal days; solar cells still collect juice on slightly cloudy or overcast days, but this method doesn't work nearly as well.

Still, a good way to apply solar energy when in conditions that permit. I'd like to set up a small unit with a fresnel lens and 'boiling globe' to generate hot water (which I'll pump through a radiator) for my house in the winter. The problem I see is with safety, that beam has to be EXACTLY where I want it or I'll burn the house down.

Re:It's being done!

They're building a huge pane of glass on the Australian desert. This pane of glass is supended a few feet off the ground, which is painted black. The air between the glass and the ground is heated, and since hot air rises, it travels toward a chimney at the center of this contraption. As it moves through the chimney, a large turbine generates the necessary power. This odd design works extremely well, but requires very bright, sunny locations that don't mind a glass pane a square mile wide!

Re:It's being done!

Sounds like it has a lot of advantages - like simplicity. The turbine of course is full of stuff that can break, but the rest of the whole operation has no moving parts, which is a big plus. Scaling up has to be fairly easy as well - just add a turbine and extend the size of your glass farm.

Regular solar arrays need to have panels or mirrors that track the sun - lots of stuff to break over a large area, fancy focusing algorithms and sensors and motors...

Often simple is best with stuff like this - that's how many home solar heating systems work - forget completely replacing the grid, just pipe some water through panels on the roof to heat it up...

Re:Ideas

Right. A smaller cell that could absorb the focused light would be more efficient and probably cleaner and more efficient to produce or operate. The issue I was addressing is that you can't really increase the output from the solar cell because you are still limited by the amount of light entering it. Consider this: A flashlight (with beam having a low divergence angle) is shining on a large perfectly efficent solar cell. All of the light is converted to energy. If the same (wide) beam is focused down to a perfecly efficient solar cell that is 1/100 the area of the larger cell, you will see the same energy. To obtain the full energy of the flashlight's beam, the lens would have to be at least as big as the beam cross section at their intersection in space. A cell of that same area as the lens would (theoretically) receive the same power from the flashlight.

So I agree with timmi. But remember that the ore optics you have in your system, the less light will reach the photovoltaic cell. Optics are not perfect. (By the way, mirrors are lighter than lenses, and are easier to build and control.)

Re:Ideas

Here [mdatechnology.net] are a few [nasa.gov] references [photonics.com] to increasing solar cell output with Fresnel lenses. Enjoy!

Re:Ideas

From one of the articles: "Cylindrical Fresnel lenses provide a 7:1 concentration, allowing a single multijunction GaInP2/GaAs/Ge cell to collect solar energy equivalent to that gathered by seven cells."

In other words, a fresnel lens does not help in terms of energy gathering. On a cost or mass per area, it does.

A good use

Maybe not very practical, but it might make a good paint remover. I have seen work crews remove paint from wood surfaces with a heat gun that looked like a big hairdryer, so I would think this type of lens would be helpful for stripping paint off metal surfaces such as water towers and so forth.

Terrorism...

I wonder what his Terrorist Quotient is? [slashdot.org].

A use for AOL CD's

A friend and I were discussing what to do with all of our AOL CD's. We both came up with the idea that you could make a similar device out of them.

Welcome! You've got fire!

All we need now are...

Sharks with...giant Frensel Lenses attached to their heads!

Giant Fresnel Lens ...

Meet Brood X of the 17-year Periodical Cicada.

Snap! crackle! pop!

Why waste such a monster on mere ants. I realize there are some of you out who would think of a certain movie and popcorn (lots of popcorn), but you've got to agree this is more unique.

If only I had this as a kid

This is just like the magnifying glass and ant game only this scales up to poodle sizes. Oh well. If I ever have a son...

Mindless

Chalk actually burns under this thing.

Chalk burns eh? Creative chemistry, more like it. Here's another fun thing you can do: drop your "burnt" chalk in a glass half-full of water, let it bubble, and put your finger in it. Let me know how it feels.

So do aluminum cans. They smell really bad.

Aluminium doesn't smell bad when it burns. I suspect whatever soda pop chemicals remaining in the can do.

It seems that normal concrete will start emitting plumes of smoke just before it pops

As would burning tar, or any other heavy petroleum derivate.

* Mike's car.

Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

Try focusing the lens on the round plastic thing that smells funny, on the rear side of the car...

Seriously, this article is all about playing with a new destructive toy and not much about using the toy in question to do interesting science-related experiments.

Re:Mindless

Chalk is limestone. If you burn it, you get lime (calcium oxide). Add water, and you get calcium hydroxide. It's a very strong antacid.

Re:Mindless

antacid= Base, which is worse for skin than acid, Acid you will feel and pull your hand away because the human body can feel the burn from acid, a base will eat through your skin and you will just feel "slippery" s it turns your flesh into soap

Re:Mindless

I don't know what you were doing in chemistry (probably wearing the proper equipment) but lye burns like all hell once it gets through the first couple layers of skin.

Re:Mindless

this article is all about playing with a new destructive toy and not much about using the toy in question to do interesting science-related experiments.

Yeah, and I guess it shouldda been Smiley Captioned for the Humor Impared, too.

...and?

Playing with a toy is the POINT of a toy. I have a new Radeon 9800 Pro that, I am made to understand, has a pretty bitching vector unit that can be used for scientific calulations, rendering and the like. It is not used for any of these educational pursuits, however, and is instead used to render lightsabers which I then use to cut up bad guys it also renders. In other words, I bought it as a toy.

It doesn't sound to me like they ever intended to do much science, it sounds like they intended to fuck around and burn shit, which they did with a high degree of success.

Re:Mindless

1) Aluminum cans have a thin coating of plastic on the inside to provent the soda's acid from etching the aluminum. 2) they have all sorts of paint on the outside. That's what smells bad. Not left over soda.

But, onto the other point: many geeks like high amounts of kinetic energy. It's true. Often, this love tuns into the irrational lust for wanton destruction of random objects. Sometimes, something is learned by the results, sometimes not. But it's the journey that's important (fun).

Re:Mindless

But, onto the other point: many geeks like high amounts of kinetic energy. It's true. Often, this love tuns into the irrational lust for wanton destruction of random objects.

Which leads to my observation that, when presented with a large electromagnet, a REAL geek immediately constructs a railgun

I mean, really. Is there anything more beautifully destructive than a railgun?

popping concrete et al

It seems that normal concrete will start emitting plumes of smoke just before it pops
As would burning tar, or any other heavy petroleum derivate.

Concrete doesn't contain the slightest amount of petroleum. You're thinking of -asphalt-, which is entirely different.

What smoked was contaminants on the surface of the concrete, and possibly some stabilizers. It popped because of the moisture in the concrete expanded- concrete doesn't handle much except external compression very well.

Aluminium doesn't smell bad when it burns. I suspect whatever soda pop chemicals remaining in the can do.

No, more likely the label ink.

Re:Mindless

It seems that normal concrete will start emitting plumes of smoke just before it pops

As would burning tar, or any other heavy petroleum derivate.

concrete [reference.com]: "A hard, strong construction material consisting of sand, conglomerate gravel, pebbles, broken stone, or slag in a mortar or cement matrix."

I do not think that word means what you think it means. It seems as if you are confusing concrete with asphalt [reference.com] or tarmac [reference.com](adam).

Guess what, setting shit on fire is fun! If you are relatively responsible about it and don't light shit on fire accidentally and/or let things get out of hand (note: many forest fires grow from the cooking campfires of the incompetent) then really, who are you harming? Well, anyone breathing the vapors. But besides them?

I have one of these.

I found one of these at my school last year. The first thing I did was take it to the parking lot to set paper on fire. The asphalt under the paper burned. I also melted pennies with it, and it can make holes in soda cans. Is there anything else anyone thinks I should burn with it? it's in my garage.

Re:I have one of these.

Is there anything else anyone thinks I should burn with it? it's in my garage.

That depends. Do you happen to live near Lindon, Utah [sco.com]?

Laser Communications

Besides destorying things, these fresnel lenses cand be used for all sorts of constructive fun.

A perfect example is a laser communication system. A laser beam can be modulated and used to transmit audio. The receiver needs to collect as many photons as possible from the laser transmitter - hence the use of the fresnel lense. Signals can be bounced off clouds - I've heard of transmissions going over 60 miles!

The Amatuer Radio Laser Communications Page [qsl.net] has a good primer that has a link to a lot of the basics. And no, you don't need a ham license - although it helps!

Hanging wall art

Hanging a Fresnel Lens in front of a white wall projects a nicely focused image of the room onto the wall. Depending on the arrangement of the room and windowage, its poosible to watch the world pass by on projected image. The optimum distance from wall to lens is approximately the focal length (or a little farther if the subject is close to the lens.

Just make sure the sun never gets to the lens or it will burn an arc across the wall.

If you like burning up stuff with a lens...

you'll love this flash game: Ant City [channel4.com]

$99 for the cheap fresnel...

Could you do something serious with this? Put the damn thing in a rig that follows the sun, and a small steam turbine under it, just how much juice could it provide?

I wish I knew the math to this, but damn, if it could provide even a small fraction of the power I use during the daytime... (by this, I mean 5-10%)

Anyone want to impress me with their math/physics skills?

Re:$99 for the cheap fresnel...

If you follow the sun perfectly you could figure on about 1 kW of light (cheesy rule of thumb) hitting your turbine. Assume 30% efficiency and you have 300W of electric power generated for an average of 12 hrs per sunny day. Three light bulbs (or 6-8 florescents) or one fully loaded computer (300 W power supply, no electric heat, iron, or oven. Oh and you'll need a capacitor bank to handle your inductive load when motors start. Go grab your power bill and see how many kW/hrs you use in a month and then figure out how many fresnel lens/turbine array's you would need to achive that power. Storage would be a mofo, although you might be able to sell it into the grid in your area.

Re:$99 for the cheap fresnel...

I wish I knew the math to this, but damn, if it could provide even a small fraction of the power I use during the daytime... (by this, I mean 5-10%)

- In bright summer daylight, at noon the sun provides 1200W/m2

- This fresnel lens is 80x100, so captures 1200 * 0.8 = 960W at best

- A good steam engine, with a condenser and exhaust reheater provides has an efficiency of about 30%, so it would give 960 * 0.3 = 288W in mechanical power

- A good alternator, going at its preferred RPM (not necessarily that of the steam engine's prefered RPM, but let's assume) has an efficiency of about 90%, so it would give 288 * 0.9 = 260W

So you'd get 260W in the best possible conditions, in the brightest of days, in summer, at midday. Throw some clouds and, assuming the entire thing doesn't stall and stays at its nominal efficiency (not likely, but let's assume), you get about 6 times less power, so about 43W

In short, you're better off with solar panels: perhaps a little less efficiency for the same price, but more surface and a lot less aggravation.

Would this be possible?

Would it be possible to build a giant one, say 100 square feet, and focus it into a fiber optic type of cable, essentially using it for a cutting laser?

Or what if you had a few massive ones in space, could you focus enough energy for use in a fusion reactor? You'd amplify all of that free energy and I don't really know what I'm talking about. Perhaps you could attach it to a shark's head.

Re:Would this be possible?

Something like this? [go.com]