A set of pure tones having the following frequencies is produced one after the other: 8Hz, 500Hz, 25kHz, 15kHz, 0.05kHz, and 40kHz. Answer the questions that follow.
(i) Classify every listed frequency as infrasonic, audible, or ultrasonic for an average human listener.
(ii) Select any two frequencies from the ultrasonic category and describe one industrial or medical use of ultrasound for each chosen frequency.
(iii) Explain why ultrasonic waves are preferred in the applications mentioned in part (ii).