Materials that convert sound into electricity (and vice versa) are called _____ or _____.

• A. Piezoelectric or Ferroelectric
• B. Magnetic or Conductive
• C. Acoustic or Optical
• D. Thermal or Piezoelectric

Answer: (A)

The main idea is piezoelectricity: certain materials generate an electrical signal when they are mechanically stressed (like when sound waves push on them) and, conversely, they deform when an electric field is applied. This two-way conversion is exactly what lets sound become electricity and electricity become sound. Piezoelectric materials include common examples like quartz and various piezoelectric ceramics, and ferroelectric materials are closely related since they share a non-centrosymmetric crystal structure that produces strong piezoelectric responses; in other words, all ferroelectrics are piezoelectric, so they’re often treated as alternative names for this behavior. That’s why the correct pair is piezoelectric or ferroelectric. The other options don’t describe materials that convert mechanical energy into electrical energy in this way.