|MadSci Network: Engineering|
Hi, Carolyn: Not knowing what grade level you are, we’ll start with the basics and work up from there. All ordinary flashlights, such as the ones you may have around your house, need just a few things to make them work: 1) An electrical power source - a battery. 2) A way to change the electricity from the battery into light - a light bulb. 3) A way to get the electricity from the battery to the light bulb - wires. 4) A way of turning the light on and off - an electrical switch. 5) A way to aim the light - a reflector. Get your parts together. For your flashlight, you will need a battery (a flashlight “D” cell is fine), a 1 ½ volt flashlight bulb, a small board (about 4” by 6”) to mount the parts on, some duct tape, some insulated copper wire (it doesn’t have to be heavy-gauge; normal “hook-up” wire will do – about 2 feet long, some aluminum foil, some thin cardboard, some fine sandpaper, and 2 thumb tacks. Drug, variety, and super-markets will usually have the battery and replacement flashlight bulbs. You must get a bulb that is rated at 1-½ volts, because that is the voltage produced by the battery. Sometimes they will label the bulbs by the number of batteries you are using such as: “… For flashlights with 2 “C” cells”. In that case, you would get one that says: “… For flashlights or penlights with 1 cell.” Don’t worry if it says size “AA” or “A” or “C” or “D” because the battery we are using, a “D” cell, has enough power for any of them. The “D” cell is the big, fat one you find in flashlights. The “AA” or “AAA” batteries are the small, skinny ones you would use in toys or portable radios. All 3 will provide 1 ½ volts, but the larger “d” cell will last much, much longer. It’s like comparing a 12-ounce can of your favorite soft drink to a 2- liter plastic bottle of the same soft drink. The 2-liter bottle will obviously last longer, providing you drink each at the same speed. Let’s start assembling. Cut the wire into 3 pieces. Make 1 piece 1 foot long, and the other 2 pieces 6 inches long. Strip one-half inch of insulation from both ends of all three wires. Use a wire stripper or knife (BE CAREFUL!). Tape one end of the 12” wire to the bottom of the battery, making sure you have good contact between the copper of the wire and the metal base of the battery. Tape one end of a 6” wire to the top (the ‘button’ end) of the battery. Again, make sure you have good contact. Make a small loop on the other end of the 6”wire you just attached to the battery, and on one end of the other 6” wire, which isn’t attached to anything yet. Tape the battery to the board, being careful not to pull the wires loose. If the thumbtacks are painted, use sandpaper to remove the paint from the top of them. You must use metal thumbtacks. The plastic “push-pins” won’t work because they will not conduct electricity. Take a 2-inch square piece of aluminum foil and fold it in half, then fold it in half again until you have a strip two inches long and one-half inch wide. This is your switch. Push one of the thumbtacks through one end of the strip, about one-half inch from the end, and slip the loop of the wire from the battery around the tack. Push the assembly into the board. Take the second thumbtack, put it through the loop in the end of the wire that isn’t attached to anything yet, and stick it into the board right under the free end of the aluminum foil strip. Make sure you place it so the foil will touch the top of the thumbtack when you press down on it. That completes the switch. Now attach the free ends of the wires to the bulb. Strip another 1” of insulation from the long wire coming from the battery, and wrap it tightly around the metal base of the bulb. Secure it with duct tape. Make sure you cover the whole base of the bulb with tape EXCEPT for the little blob of solder on the very end. Place the end of the wire that comes from the foil switch, lay it directly over the solder blob and secure it with duct tape. You now have a working light source. To test it, press the foil strip down so it touches the head of the other thumbtack. That’s called closing the switch. The bulb should light. If it doesn’t, there are only three things that could be wrong: 1) One or more of your connections is bad, or 2) the battery is low or dead, or 3) the bulb is burned out. Check those items in the order given. Now that you’ve gotten the bulb to light, lift the foil so it doesn’t touch the other thumbtack. That’s called opening the switch, and the bulb should go out. But wait! You still don’t have a flashlight. When the bulb was lit, the light went in all different directions – It doesn’t help much to be able to light up a whole room when all you wanted to do was light a path for you to walk at night! You need to gather all those beams of light and make them point in the same direction. That’s where the reflector comes in. To make it, coat a 4” square piece of thin cardboard with rubber cement or white glue, lay aluminum foil over it - shiny side up, smooth out any wrinkles, and let it dry. Turn it over so the foil is face down, and draw a trapezoid (look it up in a dictionary or math book), as shown below. Cut out the trapezoid and gently curve it, foil side on the inside, until the two same-size sides meet. You want to end up with something that looks like a funnel - a small hole on one end for the bulb, and a large hole on the other end for the light beam to come through. Put tape around the outside to hold its shape. The small hole will be large enough so you can move the bulb in or out of the cone. Try several different positions and see how it changes the pattern of the light. Good luck, and have fun!
Try the links in the MadSci Library for more information on Engineering.