Experiment 4

Rejecting Counterfeit Coins

Materials: Iron bolt 2” long with nut and 2 washers. 20’ of hookup wire. Thin, stiff cardboard 10” by 12”. Telegraph key from Experiment 2. Various coins and coin-sized washers (slugs). 6-volt battery.

     WINDING THE ELECTROMAGNET. Place a washer at each end of the bolt and engage the nut. Wind at least four layers of wire between the washers. After you’re done, twist the loose lengths of wire a few times to keep the electromagnet from unraveling.

     PREPARING THE SETUP. First, put marks on the cardboard to indicate front, back, top, and bottom. Then draw a centerline down the length of both the front and back. Also draw a parallel line on the back l/2” to the right of the centerline. Tape the electromagnet on this parallel line about 1/3 of the way from the top.

     On the front, glue an A-shaped piece of wood as a divider. Locate it a few inches from the bottom, and position the peak l/4” away from the center- line, toward the electromagnet.

     Now we’re going to convert the telegraph key to a switch. Very simple. Just cut a 3/4” metal disc, make a hole in the center, and put it under the free screw. Also straighten the arm, and bend the end upward. The switch will be “on” when the arm is wedged under the disc.

     HEY MA, IT WORKS. After connecting the circuit, prop the cardboard against something sturdy at about a 45^o angle. From the top of the centerline, let several coins and slugs (washers) slide down the cardboard.