Make It: Conductive Speakers

Build a device that lets you test the conductivity of materials using a speaker.
By Kevin Goodwin

Ages

8-13


Conductivity is a measure of a material's ability to conduct an electric current. Enlist your tween's help in building a device that lets you test the conductivity of materials using a speaker.

Materials

  • Speaker (You can take apart an old toy or electronic device that makes noise to find a working speaker.)
  • Insulated wire
  • Battery (AA size)
  • Battery clip (AA size)
  • Alligator clip leads
  • Beads, sand, or bird seed
  • Plastic lid
  • Materials to test for conductivity (cardboard, plastic, aluminum foil, nails or screws, etc.)

Step 1: Test the Speaker

Insert the two AA batteries into the battery clip, making sure they are installed correctly.

To test if the speaker works, attach the two alligator clip leads to the two metal (typically brass) clips underneath the speaker. Connect one of the leads from the speaker to one wire coming from the battery clip. Take the other lead and gently touch it to the other wire coming from the battery clip. Every time it touches, you should hear a sound as the speaker turns on. Try scraping the lead and the wire against each other. Look at the top of the speaker. What's happening? Every time the speaker turns on and off, its top should move up and down, pushing air. When the moving air reaches your ears, you should hear a sound.

Step 2: Testing Conductivity

Collect some objects you want to test for conductivity. Find things that are made of different materials, such as cardboard, wood, or metal.

Next, put some birdseed, sand, or beads directly on top of the speaker.

Test to see if your object is conductive by completing the circuit between the batteries and the speaker:  Instead of touching the alligator clip lead directly to the battery clip wire like you did to test your speaker, touch or attach it to the object. Now use the wire from the battery pack to also touch the object, but don't let the two wires touch each other.

If your material is conductive, electricity can move through it and turn on the speaker. When it turns on, you will hear a sound and see the bird seed bouncing up and down. If the speaker doesn't move or make a noise, it means the electricity isn't able to get from the batteries to the speaker and back to the batteries. There must be a gap in the circuit that the electricity can't get across because a non-conductive, or insulating, material is blocking the way.

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