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Make a glowing paper airplane when it's dark outside!
Make a glowing paper airplane when it's dark outside!
Electricity is dangerous! Read this caution.
Materials: One airplane template, transparent tape, copper tape or aluminum foil, one LED, one photo resistor (also called a photo-conductive cell), one 10K resistor, a hole punch, one paperclip, and one 3V watch battery.
Fold your plane! Directions can be found on this page.
Note: You should complete the the Light Sensitive Plane activity prior to this project.
Add the copper tape "wires," being careful to not rip or crinkle the tape.
Use transparent tape to secure each lead of the 10K resistor to the copper tape wire by the gap (see picture).
Caution: As you secure the lead near the battery, make sure your transparent tape doesn't cover the wire to the battery. Also make sure you insulate your resistor leads so they will not touch the copper wire on the opposite side of the plane.
Fold your plane together. Using a hole punch, make a hole between the two copper tape wires (running ~parallel to each other) about one inch from the back of your plane. When you reopen your plane, you should have a hole on either side (see picture).
Place the photo resistor so that the top pokes through the punched hole. Secure its leads to each parallel wire with a piece of transparent tape.
Caution: Place the photo resistor leads so they do not cross over the mid fold of the plane. Otherwise, it will be difficult to fold your wings together and throw your plane.
Up to this point, it hasn't mattered which way we place the components. However, proper placement of the LED is important. Electricity needs to pass through the 10k resistor before it passes through the photo resistor to function properly. That means that the copper wire with the 10k resistor needs to be the negative wire.
You may want to label your circuit wires so you can remember which is positive and negative (as pictured).
Use transparent tape to secure your LED to the copper tape wires. If you need help remembering which lead is the anode (+) and cathode (-), refer to the LED diagram on this page.
Add your battery and a paperclip and you're finished! You probably won't see the LED light up as you finish the project. Go into a dark room or closet to light the LED. It may be dimmer than normal but should work.
Troubleshoot
If your LED doesn't light in a room that is completely dark:
Make sure you secured the cathode (-) lead of your LED to the copper wire with the regular resistor.
Press the tape securing the leads of your components to the copper. Make sure they are touching.
Make sure the regular resistor leads are not touching the positive wire or battery. This will short your circuit.
Wiggle your LED, resistor, and photo resistor in a dark room and see if it lights.
Make sure your battery still has power.
Click to Read What's Happening
Click to Read What's Happening
Previously, we learned that resistors can be used to influence the flow of electricity in your circuit. We used a photo resistor to change the brightness of an LED based on light in the surrounding area. However, resistance decreased when light increased. This meant that the LED was brightest when it was in a bright area.
Remember that electricity follows the path of least resistance. Because resistors have materials that slow the flow of electricity, strategically placing two of them in a circuit can alter voltage. These strategic placements are known as voltage dividers.
Basically, voltage can be affected in three ways with a voltage divider:
If resistance from the first resistor is the same as the second, voltage will be halved.
If resistance from the first resistor is a lot larger than the second, voltage will be ~0.
If resistance from the first resistor is a lot smaller than the second, voltage will remain the same.
On your airplane, the photo resistor has little resistance when the surrounding area is bright. Because the 10K resistor is much larger than the photo resistor in bright areas, voltage approximates 0 and the LED has no power to light. However, when the airplane is placed in a dark location, resistance on the photo resistor increases. At some point, it greatly surpasses the 10K resistor. When this happens, voltage nears 3V and the LED lights.
To find out more about voltage dividers, see this tutorial on Sparkfun.
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