MadSci Network: Engineering


Date: Mon Jul 5 19:45:06 1999
Posted By: William Beaty, Electrical Engineer / Physics explainer / K-6 science textbook content provider
Area of science: Engineering
ID: 927392253.Eg

Hi Joseph!

When a piezoelectric crystal is bent, squeezed, or struck, it produces high voltage at very low current. This is similar to the "static electricity" created by rubbing fur on a balloon, and the current is far too low to light up an incandescent bulb or to move a meter. The high voltage can flash a small neon light, make a tiny spark, or cause a click in an amplified loudspeaker.

Common piezoelectric crystals: Quartz, Rochelle Salt, and PZT ceramic (PZT is lead-zirconate-titanate). Quartz crystals can be bought from a science store or a new-age bookstore. Rochelle crystals can be grown at home. PZT is on "piezo disks" bought from Radio Shack, or from American Science Surplus PZT is also in "electric spark" cigarette lighters and in "piezo-sparker" stove lighters.

One way to demonstrate "piezoelectricity" is to use a piezoelectric crystal to flash a small neon pilot light. American Science and Surplus sells an inexpensive kit for this experiment (request their mail-order catalog from the link above.)

Another experiment is on SCITOYS, where the spark from a piezo cigarette lighter is used to explode hydrogen gas safely.

Another experiment: glue two strips of aluminum foil to the sides of a piezeoelectric crystal, connect the strips to an audio amplifier and loudspeaker, then tap on the crystal. Every time you tap the crystal, you create a voltage impulse. The audio amplifier converts this voltage into sound, and you will here the "clack" sound when you whack the crystal.

You can grow your own piezoelectric crystal. Search the internet for "Rochelle salt" and "recipe", and you'll find websites about growing large single crystals.

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