With a Fresnel lens (see previous post) you can make a death ray – well, provided you want to kill things like pennies, or padlocks, or concrete.
Once again, Dan Rojas over at GreenPowerScience has all the fun. Take a look at the demonstrations of him doing fun things with a Fresnel lens. He boils water in just a few seconds, melts concrete (see YouTube below), and, oh yeah, there are actually practical applications like heating water and heating your house, but are those as fun and exciting as melting concrete? Heck no!
Well, you can do a few fun things with a Fresnel lens and you can do some practical things. You also can burn your yard up and your house down if you’re not careful with these things. We are using a Fresnel lens on top of a passive solar water heater to increase the heat gain. We just have to make sure the “focal point” of the lens – that is, the spot where most of the lens’ power is concentrated – isn’t directly on the tank.