In mathematics, a parabola is a conic section (roughly cone-shaped, with a rounded peak), so a parabolic mirror is a curved mirror. Parabolic mirrors and reflectors are used to collect and disburse energy, such as sound or light. Professional-grade parabolic mirrors and reflectors are used in reflecting telescopes to collect and focus light. Parabolic mirrors are also used for spotlights, car headlights and parabolic microphones. A do-it-yourself enthusiast can make a parabolic mirror to collect and focus sunlight to create a functional solar cooker. Made of common items, a backyard parabolic mirror solar cooker can generate lots of heat--enough to boil water on a summer day.
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Things you need
- Mirror tiles
- Satellite dish
- Adhesive gel
Remove the BUC transmitter from an old satellite dish. This is the part that extends out in front of the curved dish, focusing the satellite signal into the dish. It is easy to remove by locating and unscrewing the screws that hold the arms in place (although the exact location and number of screws will vary depending on the brand of satellite dish). You should now have a curved satellite dish on a mount or stand.
Wash the bowl thoroughly with mild dish soap and water. A clean surface will allow the (silicon-based) adhesive gel to adhere better. When the bowl is completely dry, move to the next step.
Starting in the centre bottom of the bowl, squirt a dot of silica gel and place a 2-by-2 inch mirror tile on it. (You should have 60 such titles for this project.) Let the silica bond the glass to the metal for about 20 seconds before moving to the next tile.
Repeat the gluing process with each of the mirror tiles, working in concentric circles from the outside in. It's important that the mirror tiles lie flush with the satellite dish. A parabolic mirror works when each mirror is set at the correct angle to concentrate reflected energy into one specific point. All the mirrors must be at the correct angle for maximum effect. Since the satellite dish has already been calibrated for those angles, placing the mirrors flush on the surface capitalises on the parabolic effect.
Allow the silica gel to set up completely before using the parabolic mirror. Before using, clean the mirrors with glass cleaner and a paper towel or newspaper to remove any spots, smudges or smears.
To use the parabolic mirror as a solar cooker to boil water, wait for a sunny day where the temperature is above 32.2 degrees C. Set up the parabolic mirror so the curve of the dish is facing the sun. Adjust the mirror so you can see a bright dot of sunlight reflecting on things, such as the side of the house or the fence. It is recommended that you set up a metal hook holding a thin metal container of water, such as a camping coffee pot or a No. 10 can. Adjust the parabolic mirror so the "sunspot" is on the bottom of the water container. Depending on the temperature, you can have boiling water within 10 to 20 minutes.
Tips and warnings
- Energy that reaches the Earth depends on many things: the angle of the sun, the atmospheric density and the weather, among others.
- The heat generated by a parabolic mirror can be intense. Do not let the beam of light rest on anything flammable, such as grass, wood or plastic.
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