Question

The speed of highly penetrating ultrasonic waves is:
A. Lower than those of audible sound waves
B. Higher than those of audible sound waves
C. Much higher than those of audible sound waves
D. Same as those of audible sound waves

Answer 1

Hint: The human ears can detect sounds which come in the frequency range of 20Hz to 20kHz. The sounds which have frequencies lower than 20Hz are called infrasonics while the sounds which have frequencies higher than 20kHz are called ultrasonics.

Detailed step by step solution:
Frequency of a wave is defined as the number of times the wave oscillates about its mean position per second. It is equal to the reciprocal of the time period of the wave.
Wavelength of a wave is defined as the distance covered by a wave in one time period. It can also be defined as the distance between two crests or two troughs of a wave.
Human ears are sensitive only to a certain range of frequencies of sound waves.
The hearing range of a person is from 20 Hz to 20 kHz. and in terms of wavelength, it is from 1.72cm to 17.2m.
The sounds which have frequencies below 20 Hz are known as infrasonics while the sounds which have frequencies above 20 kHz are known as ultrasonics. The highly penetrating ultrasonic waves have frequency upto ${10^7}Hz$ which is way beyond the hearing range of humans and go undetected by human ears.
Hence, the correct answer to the given question is option C that the speed of highly penetrating ultrasonic waves is much higher than those of audible sound waves.

Note: The sound waves are longitudinal waves and are characterized by the constriction and rarefaction in the medium in which the sound waves travel. Sound waves cannot travel without a medium. The range of sound waves for humans signifies that eardrum cannot vibrate at frequencies below or above the given range.