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Induction: How Many Coil Turns Do I Need?

Difficulty
Time Required Very Short (≤ 1 day)
Prerequisites None
Material Availability Readily available
Cost High ($100 - $150)
Safety When working with electricity, take precautions and beware of electric shock. Hazards: Need a parent's help using sharp tools.

Abstract

How can toilet paper help you understand the mighty power of magnetic induction? By wrapping each roll with more turns of wire, you can figure out the best way to light up a bulb.

Objective

In this experiment you will experiment with induction and test if the number of turns of wire will affect the amount of electricity in a circuit.

Credits

Sara Agee, Ph.D., Science Buddies

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Last edit date: 2013-01-10

Introduction

Did you know that the electricity induced from a magnet (electromagnetic electricity), a battery (voltaic electricity) and lightning (static electricity) are all the same? This was shown in 1832 by a famous scientist named Michael Faraday. But his most famous experiment was in 1831, when he made an "induction ring" and discovered something called electromagnetic induction: the "induction" or generation of electricity in a wire by means of the electromagnetic effect of a current in another wire (EIA, date unknown).

Faraday's experiments form the basis of most modern technology, and he is remembered as one of the world's greatest experimental physicists. He invented the first electric generator and is also known as the father of the electric transformer, the electric motor, and electrolysis. He wrote the "Law of Induction" and is known for the "Faraday Effect." Because of his important discoveries, two units in physics were named in his honor: the farad (for capacitance) and the faraday (as a unit of charge).

In this experiment you will build a simple induction circuit to test the properties of electromagnetic induction. You will change the number of turns of wire in the circuit to investigate the relationship between the number of turns and the amount of electricity that is induced. Will more turns increase or decrease the amount of electricity in the circuit?

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!

  • electricity
  • circuit
  • electrons
  • current
  • conductor
  • wire gauge

Questions

  • How do electrons flow through wire?
  • How is current measured?
  • Does the gauge of wire effect the flow of electrons in a circuit?

Bibliography

Materials and Equipment

  • 5 toilet paper tubes
  • electrical tape
  • 26 gauge enameled magnet wire (Radio Shack sells a package with 3 spools, 1 roll each of 22, 26, and 30 gauge.)
  • scotch tape
  • very large bar or horseshoe magnet, no more than 1" in diameter (so that it will fit into the paper tube)
  • DC Microammeter:
    • You'll need an analog meter that can read in the range of 25–100 microamps of current.
    • One possibility for this project is a DC microampere panel meter by Simpson, which are available from Mouser Electronics (www.mouser.com/simpson). The nice thing about these meters is that it is bidirectional: you'll be able to see both positive and negative currents without reversing the polarity of your connections. The not-so-nice thing about these meters is that they are expensive! Any one of the following should work for this project (the 25-0-25 is the most sensitive):

      Range
      (μA)
      Mouser Catalog # Simpson Product # Approximate Price (Nov., 2006)
      25-0-25 529-04298 04298 $100
      50-0-50 529-04302 04302 $91
      100-0-100 529-04300 04300 $93

    • Another possibility is to find an analog multimeter that can read DC current in the microampere range. The disadvantage of these meters is that the needle on the meter only moves one way, so they only measure positive current. To see current flowing in the opposite direction, you'll need to reverse the polarity of your connections to the meter.
      • The B&K Precision model 114B analog multimeter will work for this project. It is also available from Mouser Electronics (www.mouser.com/bk) , part number 615-114B, approximate price $40 (Nov., 2006).
      • You can often find inexpensive vintage analog multimeters on eBay. If you decide to go this route, make sure that any meter you bid on meets the required specifications (able to read 25–100 microamps of current).

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Experimental Procedure

Note Before Beginning: This science fair project requires you to hook up one or more devices in an electrical circuit. Basic help can be found in the Electronics Primer. However, if you do not have experience in putting together electrical circuits you may find it helpful to have someone who can answer questions and help you troubleshoot if your project is not working. A science teacher or parent may be a good resource. If you need to find another mentor, try asking a local electrician, electrical engineer, or person whose hobbies involve building things like model airplanes, trains, or cars. You may also need to work your way up to this project by starting with an electronics project that has a lower level of difficulty.

  1. Wrap each tube with a different number of turns of wire: 100, 200, 300, 400, or 500. If you run out of space it is okay to overlap the turns of wire, as long as you keep the wire neat and tight. You can overlap layers of wire by winding an equal number of turns in one direction, securing it with scotch tape, and then winding an equal number of turns in the other direction. For example, when making a coil of 400 turns go 200 turns in one direction, cover the coil with a layer of scotch tape, and then go 200 more turns back in the other direction.
  2. Leave about 3 inches of loose wire on either end of the coil for making connections with the ammeter to measure your current. Use scotch tape to wrap around and secure the wire tightly, so that the coil does not unravel.
  3. Get your parent's help to scrape off 1/2 inch of material from each end of the loose wire with a sharp knife. Attach alligator clips to the naked ends of the wire.
  4. Attach the alligator clips to the terminals of the DC Microammeter.
  5. Now move one pole of the large magnet into the center of one of the toilet paper tubes, starting with the coil that has the largest number of turns. What happens?
  6. Try moving the magnet back and forth in the tube. Now what happens? Is there a difference when you move it fast vs. slow? Does the direction of movement make any difference?
  7. Try the other pole of the magnet. Now what happens?
  8. Determine the best way to generate a current in your experiment, which magnet you will use, which end, and how you will move it around. Keep these the same for each of your experiments as a control.
  9. Test each coil by placing it around the steel bar and measuring the number of microamps produced. Use the DC microammeter according to the manufacturers directions, and write down how much current is produced by each coil, measured in microamps (μA). Use a data table to record the results for each coil:

    Coil Number of Turns Current Produced (μA)
    1 100  
    2 200  
    3 300  
    4 400  
    5 500  

  10. Make a graph and analyze your results.
  11. Which tube produced the most electricity? How did the number of turns of the coil relate to the amount of electricity that was produced?

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Variations

  • Try using different materials to induce a current in your circuit. Try comparing steel, iron, copper, nickel, aluminum, or any other metal rod you can find at your local hardware or hobby store. Which rod materials work the best? Are there any materials which do not work? What do you think this means?
  • You can use the same principle of magnetic induction to build a very simple generator. Try the Science Buddies project Shaking Up Some Energy to see how it works.
  • You can also use a similar circuit to make an electromagnet. Try the Science Buddies experiment Magnets and Charge or Measure Your Magnetism to see how the number of turns can affect the strength of the magnetic field.

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