Final answer:
A transducer, using the piezoelectric effect, generates ultrasonic waves in modern fathometers. These high-frequency waves are beyond human hearing and are utilized in medical imaging and sonar technology.
Step-by-step explanation:
In modern fathometers, the sonic or ultrasonic sound waves are produced electrically by means of a transducer. The transducer contains a crystal that exhibits the piezoelectric effect, which is the expansion and contraction of a substance when a voltage is applied across it. This effect causes a vibration of the crystal, emitting high-frequency ultrasonic waves.
These ultrasonic waves are essential in various applications, such as noninvasive medical diagnoses like observing a fetus in the womb, as well as in sonar systems used by bats, dolphins, submarines, and some birds for navigation and locating prey. The ultrasonic waves operate at a frequency range that is higher than the highest frequency humans can hear, typically from 30.0 to 100 kHz, and are used to provide critical data based on the reflections and Doppler shifts of the waves.