Question

why do we prefer ultrasonic sounds over other frequencies like x-rays for medical application.

Answer 1

it's because the ultrasonic waves doesn't tend to damage our cells but x Ray's are electromagnetic wave which have 60% chance of damaging our cells

Answer 2

ULTRASONICS : Inaudible sounds having frequency more than 20000Hz are known as ultrasonic. Examples Animals like dolphins, bats, porpoises, moths of some families, dog, children under the age of five, rats etc.  APPLICATIONS OF ULTRASOUND : Ultra sound waves have high frequency and very short wavelength. Hence they can be used in ;- I INDUSTRIES :   (a) CLEANING AGENTS: Ultrasound is used to clean particles of dust, grease and dirt present in parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the their high frequency they stir up the cleaning solution as a result the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned. (b) Ultrasounds can be used to detect cracks and flaws in metal blocks.Metallic components are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. The apparatus consists of a transmitter and a detector. Transmitter allows the Ultrasonic waves to pass through the metal block and detectors are used to detect the transmitted waves. If there is no defect in the block then the waves pass through it and are received by the detector but if there is a defect then the ultrasound waves get reflected back from that defect/crack Ordinary sound of longer wavelengths cannot be used for such purpose as it will bend around the corners of the defective location and enter the detector.