Casey Rutherford, age 12, of Mesa, Ariz., for his question:

HOW DOES A TRANSDUCER WORK?

A transducer is a device that converts electric waves into mechanical vibrations, or vice versa. You'll find transducers in microphones, loudspeakers and phonograph pickup cartridges.

Transducers work in various ways. Many phonograph cartridges use piezoelectric materials that produce voltage when squeezed. Loudspeakers use electromagnets that vibrate when current flows through them.

Some ultrasonic transducers use magneto restrictive materials that contract in a magnetic field. Ultrasonic transducers generate and detect vibrations above the frequency range of human hearing. They are used to clean delicate instruments, to drill oil wells and to measure the level of liquids in the fuel tanks of space vehicles.

Sonar transducers send and receive sound waves in water.