See Also: Calah(encyclopedia)

piezoelectricity (sh) and Calah (sh)


piezoelectricity (sh)




Appearance of an electric field in certain nonconducting crystals as a result of the application of mechanical pressure.

Pressure polarizes some crystals, such as quartz, by slightly separating the centers of positive and negative charge. The resultant electric field is detectable as a voltage. The converse effect also occurs: an applied electric field produces mechanical deformation in the crystal. Using this effect, a high-frequency alternating electric current (see alternating current) can be converted to an ultrasonic wave of the same frequency, while a mechanical vibration, such as sound, can be converted into a corresponding electrical signal. Piezoelectricity is utilized in microphones, phonograph pickups, and telephone Communications systems.


Calah (sh)




modern Nimrud

Ancient city, Assyria.

Lying south of modern Mosul, Iraq, it was founded in the 13th century BC by Shalmaneser I. It remained unimportant until the 9th century BC, when Ashurnasirpal II made it the capital of Assyria. It was the site of a religious building founded in 798 BC by Queen Sammu-remat (Semiramis of Greek legend). Excavations there have yielded thousands of carved ivories from the 9th-8th centuries BC.