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ArcticMyst Security by Avery

Question about the sun and magnifying glasses

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Wikipedia gives the solar constant at 1,370 W/m[sup]2[/sup] at it's zenith. The earth's atmosphere absorbs some of the energy lowing the value to ~1kW at ground level. Now you need to factor in that the glass transmits only ~90% of visible light. and as for invisible light... you never know. You'll probably only end up with 700W MAX. Even then, that's white light, and nothing but black with absorb most of it. It's a pretty neat idea, but a piece of glass that big and precise may cost it's weight in silver. Fresnel lenses twice that size can be found on ebay for $100 or less.

darklandz said:
i remeber literally setting some tissue on fire with the sun/magnifying glass trick - yet even a >400mw green laser wont put a single scratch on a white tissue?

That's partially because of the sheer power, and partially as a result of the invisible wavelengths.

likewhat said:
A microwave oven takes like 2 or 3 minutes to boil a cup of water and it is 1 kW.

Keep in mind that's power consumption, not power output. Only lasers are rated by power output, all other EM devices (that I'm aware of) are rated on input.
 





L

likewhat

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Yeah, it might be rated on input, but magnetrons are really efficient unlike lasers so it is still about 1 kW
 
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Magnetrons are about 65% efficient. You'd be like WL if you said 650W is ABOUT 1kW
 
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there was a mythbusters not to long agow when they tried to use sevelral concave mirrors to set a wooden ship on fire, but they failed :(
 
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The largest fresnel lens I have a source for is at the below link.  When you guys start transmuting elements or something cool like that, PM me!  LOL  -Glenn
Put "fresnel" in the search que upper right corner.
http://www.sciplus.com/search.cfm
 




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