Solar furnace science experiment?

Question

When building a tiled, parabolic surface, is there an equation used to determine the angles of the mirrors?

Answering my own question.

Equations for "focal length" could be useful, but the device is focused when mirrored tiles are tilted individually, until all the bright spots of reflected light are aligned into one, tight space.

As to be expected, ideas for pivoting every, individual mirror are either mickey-mouse or prohibitively expensive.

Any full length mirror could be cut into pieces and adapted for this purpose.

Protective goggles will actually be useful, not for flying splinters, but because there will be much reflected light from any burning target.

Even small pieces of metal can melt in refractory ovens, but the idea is used to conserve cooking fuel in remote regions throughout the world.

Answer 1

Think about what you want the mirror to do. You want it to reflect incoming light from a distant source onto a specific target. You know that the angle of incidence equals the angle of reflection. Draw a diagram showing the mirror and the light path and label the angles. A little geometry will tell you what the angle needs to be. Do this carefully and keep your notes. It is a valuable part of the experiment.

See the reference if you choose to use a parabolic shape. Look particularly at the properties of the tangent, since the tangent is really the angle of the mirror at that point. If it really does focus all incoming light at the focus, prove that and include that in your report.

A practical focusing solar collector should either track the light source, or be designed so that it works reasonably well as the sun moves across the sky over time. A trough rather than a cone works better that way for a non-tracking collector.

If you're building a tiled collector, there's no particular reason to use a parabola. Pick something that you can reasonably and practically build, and then calculate the correct mirror orientation for each location. Just cover the sunny side of your house with mirrors and focus them on the black box. But don't set your neighbor's house on fire!

Answer 2

Just make sure the mirrors are tangent to the parabola. The greater number of mirrors, the closer you will be to a perfectly parabolic mirrored surface which, I gather, is what you're seeking.