Sound with frequencies above 1 MHz attenuate ______.

• A. Entirely
• B. Not at all
• C. Partially
• D. Only under certain conditions

Answer: (A)

High-frequency sound loses energy much faster as it travels because the mechanisms that turn mechanical energy into heat—viscous losses, thermal conduction, and scattering—become stronger with frequency. When the frequency climbs above about 1 MHz, these losses are so large that the wave’s amplitude decays to negligible levels over practical distances, effectively preventing propagation. So, sound above 1 MHz is considered to be completely attenuated in typical propagation scenarios. The idea that there would be no attenuation would ignore this strong frequency-dependent loss, and suggesting only partial attenuation misses the rapid decay seen at these ultrasonic frequencies, while mentioning special conditions would imply exceptions that aren’t part of the general behavior.