Ultrasound refers to a sound wave with a frequency greater than the upper limit of human hearing, which is generally over 20 kHz. In general, humans can hear sounds with a frequency between 20 Hz and 20 kHz.
Impact crater is a type of impact landform formed due to collision of astronomical objects. Impact crater is a circular depression formed by the hypervelocity impact of a smaller body. Impact craters should not be confused with landforms like sinkholes, glacial cirques which are different in composition and origin from the impact crater.
EXAMIANS