The Piezoelectric Effect
Some of the crystals are piezoelectric, for example quartz. An electric charge can be produced when these crystals are compressed or hit. And if an electric current is applied on these piezoelectric crystals, their shape can be altered accordingly. The piezoelectric property provides these special crystals possibilities for usages in many fields.
One typical application of piezoelectricity property is in quartz clocks and timers. Different size of quartz crystals will vibrate at different rates, and detectable electrical pulses can be produced when the crystals vibrate back and forth. A quartz clock can keep time through a small precisely cut crystal. The quartz crystal can be kept vibrating forth and back by a special circuit called an oscillator, via adding calculated amount of electricity to its pulses. The number of pulses produced by the quartz crystal will be counted by the clock and taken to measure seconds, minutes and hours.
Another important application of piezoelectricity is in capturing and generating sound. For example, piezoelectric pickups are already widely applied in folk guitars and other acoustic devices. A piezo pickup is a strip shape material attached onto the device and connected to two wires. The piezo pickup will vibrate with the sound when the device is played, and these vibrations will produce an electrical current, which can be recorded and further amplified into louder sound.
Compared to the piezoelectric pickup, a piezo speaker works in the opposite way. When an electricity is applied to a scrip of piezoelectric material, the material will vibrate forth and back, producing pressure waves in the surrounding air, and these waves are just the sound we can hear.
Piezo lighter is a typical visible applications of piezoelectricity. Almost all lighters with a push button is triggered by piezoelectricity. A tiny spring-powered hammer will protrude from the surface of the piezo crystal when the button is activated, and when it reaches the head, the crystal will be released and struck by the hammer while the gas is switched on. This process can produce a large voltage in the crystal and the electric voltage will pass into two wires nearby. This large voltage can create a spark amid the two wires, such igniting the gas. This piezo igniters are still utilized in many gas furnaces and stoves too.