You can demonstrate the Piezoelectricity using this two component circuit. Just connect a high bright transparent LED to the Piezo element and gently tap on it. You can see the LED flashing without a battery power. Try and make a Fun.
Piezoelectricity is the phenomenon in which piezoelectric materials generate a minute voltage when mechanically stressed. The piezoelectric effect is due to the asymmetry in the crystalline structure of the piezoelectric materials. A good example is the Lead Zirconate Titanate crystals used in the Piezoelement of Buzzer. This can be used to demonstrate piezoelectricity. The Piezoelement behaves in two fashion. When it is subjected to an electric potential, it vibrates due to Indirect Piezo electric effect and produces sound. This is the principle in the working of Piezo buzzer. But if the Piezoelement is subjected to heat or mechanical stress, it generates around 1-2 volts through Direct piezoelectric effect.
In the Piezoelement, the white coating on the circular plate is the Piezo material and is the Positive. The Rim of the metal plate is negative. Just solder the LED’s anode to the centre part and the cathode to the rim of the Piezoelement. Care should be taken while soldering. Since the material is a thin film, it may detach from the plate. So just apply solder once. Paste Cellotape over the solder joints to prevent its separation.
Just tap on the white part, LED will blink. If the tapping is strong, brightness of LED increases.
You can purchase a 40 mm Piezoelement at the cost of Rs.5 or procure it from a damaged buzzer. Size should be large. Experiment with more elements connected in series and place it on the case of a vibrating Mixi. See what happens?