QUE : WHAT ARE PIEZOELECTRIC CRYSTAL AND PIEZOELECTRICITY ?

 SOL:  PIEZOELECTRIC CRYSTAL  A dielectric crystal in which dipoles aligned in an ordered way and produce some resultant dipole moment is called piezoelectric crystal.

PIEZOELECTRICITY  When external pressure is applied on piezoelectric crystal electricity is produced and is called piezoelectricity. The mechanical stress leads to displacement of ions in crystal which results into electricity. if crystal is placed in electric field then mechanical stress is produced due to displacement of dipoles. example pickups in record players.