If Junior wants to take home the Blue Ribbon in the science fair, there’s plenty of inspiration to be found in the April 1941 issue of Popular Science. Some of these ideas might look difficult to some kids today, but the smart students will realize that they are really quite simple. One or more of these ideas is sure to impress the judges.

The idea shown above is a simple buzzer. When the battery is connected, the electromagnet pulls the strip of metal away from the screw. This breaks the contact, and the strip snaps back into place, and the whole process is repeated.

Shown at left is a simple thermostat.  It’s made of a strip of iron and a strip of copper or brass, bolted together.  When the temperature changes, they expand or contract unequally, causing it to bend to one side.  Simply add an electrical contact at just the right spot, and a circuit will turn on or off at a given temperature.

The self-explanatory experiment to the right uses a thin strip of foil to demonstrate how a fuse works.  Simply cut it narrow enough so that it blows when a short-circuit is applied.

The experiment shown below is similar to one we featured recently.  It uses a transformer designed to convert 120 volts to 6 volts, but shows that the process can be reversed to change a low voltage to a high voltage.  As in the experiment we showed earlier, a wire is run along a file to create a pseudo-alternating current at the low voltage.

The final experiment is also similar to one we’ve shown previously.  A homemade microphone is made by balancing a pencil lead on two razor blades.

Even though all of these experiments use the old-school large dry cells, they will work just as well with alkaline D cells.  The hookup will be easier if you purchase battery holders.  And don’t forget some wire.

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