Lighting Fires with Lemons

We all know that you can stick copper and zinc in an acid and make a battery. And the classic demonstration of this is with a lemon. YouTuber [NorthSurvival] takes this to an extreme — starting a fire by shorting his lemon battery across some steel wool. (Video embedded below.)

Now calling this a “survival tip” is pushing it. A lot. When’s the last time you went camping with a bunch of zinc and copper nails, much less a supply of fresh lemons? It might be easier to put some matches in a waterproof canister, or just bring a lighter. But when the zombie apocalypse comes, and all the lighters are used up, the man with a lemon tree will be a millionaire.

Seriously, though, this demo made us question a few assumptions. First, when people do the potato- or lemon-battery experiment, they often use multiple lemons. Why? Hooking the pins up like [NorthSurvival] did in series seems like a no-brainer after the fact.

And the lemon seems to be putting out a fair amount of juice (Amperes, that is). We’ve got to wonder — what is the short-circuit current of a lemon battery? And why haven’t we seen specs anywhere? What kind of “science education” experiment is this anyway, without measurements?

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You know that they say about guys with big lenses?

[Tony Lovell] and [dkpeterborough] built a sizable camera lens using optics from a flight simulator projector. What they ended up with is a 900mm lens that can make a beautiful photo of the moon, or capture distant landscapes in great detail. The body of the lens was designed in CAD and sent off for fabrication out of aluminum, as seen above. The concentric baffles help to prevent lens flare but it can’t be used in its bare-aluminum condition. The internals were coated using a stippling finish that leaves a sandy texture. That was covered with matte black barbecue paint, doing a great job of preventing optical interference, and the outside received a glossy white coat. Finished weight: 59 pounds, but once you see the pictures you’ll agree it’s worth lugging the bulky instrument around to grab that killer shot.

[via Make]