Solar Furnace
When I visited Uzbekistan, the first place I visited was a soviet-built research facility on the hillside in the small town of Parkent. It sounds quite secretive, and it used to be difficult to visit, but they've been more open to visitors in recent years, and we were given a tour.
The main structure is called a solar furnace, and it's basically a machine that directs sunlight to one particular point, heating that point to great temperatures. How they manage to do this is fascinating:
The main structure is in the shape of a paraboloid, which is what you get when you rotate a parabola around its access of symmetry. It's basically the same shape as a satellite dish. Only this is much larger than the average satellite dish: the mirrored surface contains over 2,000 mirrors and is 55 meters tall and 45 meters wide!
The other structure is a field of 62 heliostats, which are flat mirrors that can be turned to direct sunlight in different directions. Here's a 2D representation of what's going on:
When the machine is turned on, these heliostats are positioned at the precise angle to reflect the sun's rays directly into the paraboloid. The paraboloid then reflects all of the rays directly at one point, called the focal point. The area at and nearby the focal point can be heated up to 3,000 degrees Celsius (or 5,400 degrees Fahrenheit)! To give a basis of comparison, the melting point of iron is just 1,538 degrees Celsius.
And here's a photo of a model of the solar furnace, so you can see how the heliostats are positioned with respect to the paraboloid:
So what is this used for? Despite the fact that it could be classified as a death ray, its uses aren't quite that dark. One of its uses has been finding the melting points of certain materials and determining how well they hold up in high temperatures. In particular, materials have been tested for suitability of use in space shuttles, since temperatures during atmospheric re-entry can reach 1,650 degrees Celsius. It can also be used to generate electricity, create hydrogen fuel, and create ceramic materials.
Sample Problems
1. If the paraboloid is 45 meters wide and the depth of the center is 7 meters, find its focal length, rounding to the nearest meter.
2. The largest solar furnace in the world is located in the south of France. If its paraboloid is 54 meters wide and the depth of the center is 10 meters, find its focal length, rounding to the nearest meter.
