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💡 Beyond our hearing
The sounds we cannot hear turn out to be some of the most useful — imaging babies, cleaning parts, finding submarines.
What are ultrasound and infrasound used for?
Applications of Ultrasound
Ultrasonography and breaking kidney stones Welding, cleaning and flaw detection SONAR and locating objects
- Infrasonic (<20 Hz): detecting earthquakes, volcanic eruptions and severe storms over long distances.
- Ultrasonic (>20 kHz): ultrasonography, breaking kidney stones, welding and cleaning delicate parts.
- Ultrasound also detects defects in metal blocks and locates objects (SONAR).
🧵 Threads of Curiosity
| Frequency range | Some applications |
|---|---|
| Infrasonic (< 20 Hz) | Detecting earthquakes and volcanic eruptions; detecting severe storms across long distances. |
| Audible (20 Hz – 20 kHz) | Speech, music and everyday communication. |
| Ultrasonic (> 20 kHz) | Ultrasonography; breaking kidney stones; welding and cleaning parts; detecting defects in metals; SONAR and locating objects. |
🌎 Bridging Science and Society
- SONAR stands for Sound Navigation and Ranging.
- Ultrasonic waves are sent from a ship into the water.
- The reflected waves are analysed on their return.
- They give the distance, direction and speed of underwater objects.
- Submarines and shipwrecks can be located this way.
- Drones and aircraft hum at low frequency from their motors.
- Sensitive sound sensors detect this hum.
- This method is called audio surveillance .
Example 10.6 — A naval sonar signal sent
Signal returns after 0.90 s, so time to reach the object = 0.90 2 =0.45 s ; with v=1530 m/s , distance =1530× 0.45=688.5 m .
NCERT Question 10 — A ship searching for a
A ship searching for a sunken ship sent a sonar signal and detected an echo after 5 s. If ultrasonic wave travels at 1525 m s⁻¹ in seawater, approximately how far down in the ocean is the wreckage of the sunken ship located?
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