Question

what is ultrasound what is its use in industry why cannot we use longer wavelengths for such uses

Answer 1

ultrasounds are the sounds more than frequency of 20000Hz which we cannot hear. we can use it to find cracks and flaws inside building,bridge or others which we cannot see through our naked eyes. we cannot use other waves because they can pass through smallest of cracks but ultrasounds cannot pass, it reflects back indicating cracks and flaws