Piezoelectricity

5.4 Piezoelectricity

Electricity can be generated by exerting pressure on a crystal. A special kind of substance, the piezo electric crystal, converts mechanical energy into electric energy when pressure is exerted on it. Once a piezo electric crystal that is connected to a neon lamp is struck with a mallet, the neon lamp will emit a brief flash of light. A small portion of the mechanical energy is converted into electricity. Most of the energy is again transformed into heat. Fig. 5.4.1 illustrates the set-up.

Piezo is a Greek word for pressure. Piezo electric crystals are made of such compounds as quartz, Rochelle salt, tour-maline and barium titanate. Usually the opposite sides of the crystal are silver plated and thin, flexible copper leads soldered to the plated area. When a steady pressure is applied, no electric energy is generated. The voltage produced by piezo electric crystal is very small and cannot be measured by a voltmeter. It requires to be amplified.

Piezo electric crystals are used in record players and microphones. The piezo electric crystal in the cartridge of the pickup arm is vibrated by the record groove. These vibrations produce varying degrees of pressure on the piezo electric crystal which in turn produces varying electrical signals. These are then amplified in order to operate the speaker. Piezo electric crystals are also used to deduce pressure changes in industries and production of spark in gas lighters e.g. cigarette lighter.