Shaking Up Some Energy

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Abstract

Objective

In this experiment you will make a simple generator and investigate the relationship between magnetism and the induction of electrical current.

Credits

This project was adapted from one by J.P.Hare at the Creative Science Centre:
Hare, J.P., 2002. "Physics on a Shoestring: The Shake-A-Gen," Journal of Physics Education, September 2002, volume 37, p.436-439 [accessed: 3/18/06] http://www.creative-science.org.uk/gensimple1.html

Sara Agee, Ph.D., Science Buddies

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Introduction

One of the coolest new battery-free flashlights is the Shake N' Light. You may have seen this demonstrated on the TV, but I bought mine at Walgreen's for 5 bucks! The secret to this fun, energy-saving device is a creative way to make electricity. The Shake N' Light flashlight is powered by the principle of magnetic induction described by Faraday's Law. A magnet is surrounded by a copper coil which "induces" a small amount of voltage in the coil when it is shaken. Because the voltage is very low, there is not enough energy to power a traditional light bulb. Instead the flashlight uses a low voltage, but very bright LED. A re-chargeable battery stores the energy so that you can use it later to power your LED flashlight.

The Shake N' Light (available at Walgreen's or Geeks.com)

How does the generator work? "A generator works by a magnetic field inducing a voltage into a coil of wire. Important points to note are that the voltage increases as the number of turns of wire on the coil, the size of the coil and the strength of the magnetic field increases. The magnetic field (or the coil) needs to be in constant motion to produce/induce the electricity into the coil. This can be done by moving the magnet or by moving the coil—the effect is the same. The coil (or the magnet) needs to move in such a way that the coil continually passes through the magnetic field." (Hare, 2006)

The generator inside the shake light resembles the Shake-A-Gen, a simple device developed by Dr. Jonathan Hare at the Creative Science Centre to teach the fundamentals of electricity generation (Hare, 2002). In this experiment you will build this very simple generator made using only wire, a 35mm film canister and a magnet. All you need to do to create electricity and light the LED is shake the film can! How will the number of magnets you put in the canister effect the amount of electricity generated to light up a light?

Terms and Concepts

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• Power
• Generator
• Electricity
• Magnet
• Coil
• Charge

Questions

• How is electricity generated?
• How is the magnet used?
• Does using more than one magnet (joined together) at a time make a difference in the brightness of the light?
• Do you get twice as much light with twice the number of magnets?

Bibliography

• Here is the original source and inspiration for this project:
  Hare, J.P., 2002. "Physics on a Shoestring: The Shake-A-Gen," Journal of Physics Education, volume 37, p.436-439 [accessed: 3/18/06] http://www.creative-science.org.uk/gensimple1.html
• This additional information from the CSC describes how a crank style electrical generator is made and gives some background on how generators work:
  Hare, J.P., 2006. "Making an Electrical Generator," The Creative Science Centre (CSC) based at the University of Sussex at Brighton. [accessed: 3/18/06] http://www.creative-science.org.uk/gen1.html
• Here is another interesting experiment from the Creative Science Centre using the Shake-a-Gen to make electrical power from ocean waves:
  Hare, J.P. and McCallie, E., 2005. "Starting to Experiment With Wave Power," Journal of Physics Education, volume 40, p.574-578 [accessed: 3/23/06] http://www.creative-science.org.uk/wavegen.html
• This site has a java applet you can use to make printable, color graphs of your data:
  NCES, 2006. "Create a Graph," National Center for Education Statistics (NCES) U.S. Dept. of Education. [accessed: 3/3/06] http://nces.ed.gov/nceskids/createagraph/

Materials and Equipment

Supplies for this project are available in one convenient kit from the Science Buddies Store

• 35mm film canister
• Scotch tape and electrical tape
• Fine grit sandpaper
• Cardboard
• Scissors
• Small but very powerful neodymium magnets
• Low-current, low-voltage LED lamp. Look for an LED specified as follows: less than or equal to 2.1 volts (typical) and less than or equal to 30 mA (maximum). The lower the better for both voltage and current. Most red, green, or yellow LEDs will meet this spec. Blue and white LEDs require a higher voltage and should only be tried if you have first proven that your setup works with a red, green, or yellow LED.
• 30 guage (AWG) wire (1/4 spool, usually about 784 feet). This wire must be extremely fine in order to get enough turns in the coil (1000 turns or more). This wire should also be in a single length; do NOT splice together shorter pieces!

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Experimental Procedure

Note: Before you begin, read the first bullet point in the "Variations" section below to see if there is a shortcut you can use to build your generator!

1. Find a 35mm plastic film can and remove the lid.
2. Place the canister on the cardboard and trace around the outer edges of the circle. Repeat to make the other one.
3. Cut out the middles and edges of each circle.
4. Fit the circles snugly around the middle of the canister, spacing the two circles about 2cm apart.

   Picture showing various stages of making the generator. Shown in the middle is one of the small (but strong) neodymium magnets (Hare, 2002).

   
   
5. Wind on a few turns of insulation tape on to the can, either side of the cardboard to hold them in place.
6. Use the cardboard circles as a bobbin (or former) on which to wind the coil. Wind on 1000 to 2000 turns of thin, insulated copper wire. When you start winding, be sure to leave several inches of the inner end of the wire free so that you can connect the LED in a later step below. You must have easy access to both ends of the wire, even the one at the inside of the coil!
7. Add a layer of Scotch tape to keep them from un-winding, while leaving about 10cm of wire free at each end.
8. Scrape off some of the insulation (5mm or so) from the ends of the wire with a small piece of sandpaper.
9. Connect the ends of the wire to the LED (it does not matter which way around) by soldering the connections (if possible) or twisting the wire ends together.
10. Use some Scotch tape to secure the wire and LED to the bottom of the can.
11. Put a small (but powerful) magnet into the can and snap the lid back on.

    Close up of the Shake-a-Gen with 1000 turns (Hare, 2002).

    
    
12. Hold the can between thumb and forefinger at the two ends of the can and shake while keeping your finger on the lid to keep it from coming off. The LED should light up! It will not be a steady light though, instead it will flicker.
    • Note: If you want to design one that does not flicker you will need to include a circuit that both changes the energy generated from AC to DC and stores the energy.
13. Now you are ready to test if the number of magnets will change how bright the light will be when you shake the generator.
14. First test the generator with one magnet inside, shake, observe the brightness of the light and write the result in a data table:

15. Repeat the experiment with 2, 3, 4 or more magnets, each time writing the results in the data table.
16. Make a bar graph of your results at Create-A-Graph, a website at the National Center for Education Statistics (NCES) that has a java applet you can use to make printable, color graphs of your data.

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Variations

There are many variations for this experiment that each test a different aspect of how the generator works. Try a few:

• Another quick way to make this project is to use the spool directly, instead of using a film canister. For this to work, you need to check the inside of your spool to see if the inner end of the wire is sticking out. If it is, then here is a simple way to cheat and build your Shake-A-Gen in about 5–10 minutes! Carefully unravel about 2 inches of wire from the spool, and then re-tape the spool to secure the wire and keep it from unravelling. You should now have two ends of wire sticking up from the spool, one from the inside and one from the outside of the spool. Trace the two circular ends of the spool on some cardboard and cut out the two circles. Poke two tiny holes in one of the circles and stick the two ends of wire through the holes. Glue the cardboard down with hot-glue, keeping the wire ends out. Strip the ends of the wire with sandpaper and then attach to the LED light. Tape the light down to the lid with clear tape. Now add the magnets to the other side and glue the other cardboard circle onto the spool. Shake and see your LED light up!
• There are many different types of magnets, each with different magnetic strength. Try different sizes, strengths and styles of magnets. Do they produce similar or different results? Which ones work the best?
• Try varying the number of turns: 500, 1000, 1500, etc. Is it always true that the voltage goes up with number of turns for this simple generator? What happens when the coil gets so large that most of it is no longer very close to the magnet? Does it matter how compactly the coil is wound along the outside of the can? You might want to make a winding device for this variation to help you keep track of the number of turns you have around the canister.
• Does the thickness of the wire matter? Try using thick and thin wire, which one works best? Observe things like the brightness of the light, the neatness of the coil, the number of coils possible. What are the benefits and/or trade-offs of using different sized wire?
• Instead of using the LED to measure the electricity generated, try using a Voltmeter to get quantitative (numerical) data. Does this match your data for brightness? Which set of data is most accurate or reproducible?
• Why does the LED only shine when you shake the film canister? In this simple circuit there is no method of storing the energy produced for later use. You can build a simple storage device using a rectifier, a simple circuit to make DC voltage from the Shake-a-Gen, and a rechargeable battery or capacitor to store the energy. If you look closely at a Shake N' Light, you will see such a storage system between the light and the coil, underneath the switch plate. How does this device expand the potential usage of the Shake-a-Gen to power small devices?
• There are many other creative ways to use this simple generator to power simple devices like the Shake N' Light with motion. Can you think of your own invention? How about trying other sources of motion to power the device like wind or wave power? Here is another interesting experiment from the Creative Science Centre using the Shake-a-Gen to make electrical power from ocean waves: Starting to Explore Wave Power.
• There is another type of LED called a bicolor LED. These devices are actually two LED's contained within one package; a red and a green LED. The two LED's are wired so that one will light (say the red one) when connected one way round and the other (the green) will light when the connections are reversed (or the power is reversed). This is a common property of alternating currents (AC). What happens if you use this type of LED on your Shake-a-Gen? Is the Shake-a-Gen an AC or DC generator? You can use the Shake-a-Gen to investigate the difference between alternating current (AC) and direct current (DC). Can you build-in a moving switch to make the voltage direct (DC) instead of alternating (AC), a device called a commutator?
• If you remove the magnet from the Shake-a-Gen, you can use the generator as a "search" coil for detecting magnetic fields. Try putting it next to different appliances, like microwaves, computers, stereos, etc. to pick up electrical signals. Which appliances generate the strongest electromagnetic fields? Try putting it next to a speaker playing loud music, will the LED flash with the music?

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