Alexander Graham Bell kept working on telephone design even as phones were being installed across the US and spread throughout Europe. He read scientific journals that recorded observations, issues,  and improvements. One journal passage caught his interest: The earpiece would make a high pitch ringing noise under certain circumstances. 

At once he went to the laboratory and started experiments to investigate this idea!  In this exploration we use two coils, an “interrupter” (small DC motor), and a earphone to observe interactions. 

Preparing Materials

You can make the same observations that Bell did in a simple way.  Find the following materials:

• Copper enameled wire. This is on a wooden spool.  (any gauge will work, but #24-#30 is recommended.  Enameled wire is copper painted with an insulation coat. The ends of the wire need to be cleaned from this enamel so they can conduct electricity.) See length calculation here. (Links to an external site.)
• A tapered plastic container.
• Some tiny strips of duct tape or similar
• Sand paper
• A hobby motor
• A power source 1.5 Volt D cell
• An earphone (These are salvaged from old audio earphones!)  Test your earphone by momentarily touching the wires to the D call and listening. You should hear a click!)
Once you have these materials on your work space and have tested the earphone, 
PLEASE REPORT: Ready!  mjaeger@eou.edu