Cambridge IGCSE Physics · Syllabus 0625 · Waves
Ultrasound
What is Ultrasound?
Ultrasound is sound with a frequency higher than 20 kHz, above the upper limit of human hearing. It is an ordinary longitudinal sound wave and is not ionising radiation; its named uses are non-destructive testing of materials, medical scanning of soft tissue, and sonar.
This definition is part of the Waves chapter in Cambridge IGCSE Physics.
Ultrasound in context
Sound is produced by a vibrating source and travels as a longitudinal wave: the particles of the medium oscillate back and forth parallel to the direction the wave travels. Because the disturbance is handed on from particle to particle, sound cannot travel through a vacuum. Its frequency sets the pitch and its amplitude sets the loudness. Humans hear roughly 20 Hz to 20 000 Hz; above 20 kHz the sound is ultrasound.
Common mistakes with Ultrasound
- 22. “Ultrasound means very loud sound.” Core 3.4.9 Why wrongIt confuses the two axes of a trace. “Ultra” here refers to frequency, not amplitude. A dog whistle is ultrasonic and very quiet. CorrectUltrasound is sound of frequency above 20 kHz, beyond the upper limit of human hearing. Its loudness is a separate matter entirely. Say this“Ultrasound is sound with a frequency higher than 20 kHz.” CheckIs a 30 kHz sound necessarily loud? Explain.