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Step 11OK - Let's Burn Something!
Update: at the suggestion of foobaz utne, I flipped the Fresnel lens around so the ridges are facing the sun, and found a dramatic increase in lens performance. The secondary lens still isn't working right, but I was able to upgrade from melting zinc pennies to liquefying solid copper ones and destroying nickels!
First Test
Inspired by similar Fresnel experiments floating around the net, I decided to try melting a penny. On winter solstice, I found that a zinc penny melts within a minute when held in the focus. Solid copper pennies (from 1982 or earlier) wouldn't melt, but probably would during summer. Copper's melting point is almost 2000oF compared to Zinc's 790oF. See the first row of images for these tests.
Round 2
With the Fresnel lens oriented correctly, I had another crack at melting those coins. The following video and the second row of images shows my results. MUHAHAHAHA!!!
Note: Copper's melting point is about 2000oF, but Nickel's is 2600o. So it's highly possible that only the copper in the coin (75% copper, 25% nickel) melted, resulting in the mutilated pitted surface.
First Test
Inspired by similar Fresnel experiments floating around the net, I decided to try melting a penny. On winter solstice, I found that a zinc penny melts within a minute when held in the focus. Solid copper pennies (from 1982 or earlier) wouldn't melt, but probably would during summer. Copper's melting point is almost 2000oF compared to Zinc's 790oF. See the first row of images for these tests.
Round 2
With the Fresnel lens oriented correctly, I had another crack at melting those coins. The following video and the second row of images shows my results. MUHAHAHAHA!!!
Note: Copper's melting point is about 2000oF, but Nickel's is 2600o. So it's highly possible that only the copper in the coin (75% copper, 25% nickel) melted, resulting in the mutilated pitted surface.
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http://en.wikipedia.org/wiki/Lagrange_invariant
http://en.wikipedia.org/wiki/Etendue
This fact of geometry means A) the beam can't be perfectly parallel, like a laser -- when the rays parallel to the optical axis are all collimated, the marginal rays are diverging from the optical axis. When they're all converging... well, the size of the spot they'll produce is limited by the above optical considerations and the F-number of your system.
On the other hand, you could actually see a higher concentration (smaller spot size) in a medium with higher refractive index -- water, or oil, say. So if you want a higher-powered death ray (though one with limited range), put your subject near the focal point while in a high-index medium. (You may lose power to optical absorption, of course.)
Again, I'm not responsible for anything you do with this information -- especially dumb stuff like using a flammable optical medium (like oil, or worse)....