MP Board · Class 9 · Science · Sound(a) Distinguish between Infrasonic, Audible, and Ultrasonic sound waves based on their frequency ranges, giving suitable examples or sources for each. (b) Describe four major applications of ultrasound in modern industry and medicine.

(a) Classification of Sound Waves Based on Frequency

\nSound waves are categorized into three distinct frequency ranges:

1. Infrasonic Sound (Infrasound):

   • Frequency Range: Less than $20\text{ Hz}$.
   • Characteristics: Human ears cannot hear these sound waves.
   • Sources/Examples: Produced by earthquakes, volcanic eruptions, ocean waves, and large animals such as elephants, whales, and rhinoceroses for communication.

2. Audible Sound Range:

   • Frequency Range: Between $20\text{ Hz}$ and $20,000\text{ Hz}$ ($20\text{ kHz}$).
   • Characteristics: Sound waves within this range can be detected by normal human ears.
   • Sources/Examples: Human speech, musical instruments (guitar, flute, drum), and everyday environmental sounds.

3. Ultrasonic Sound (Ultrasound):

   • Frequency Range: Greater than $20,000\text{ Hz}$ ($20\text{ kHz}$).
   • Characteristics: Inaudible to human ears, but animals like bats, dolphins, and porpoises can hear and produce them.
   • Sources/Examples: Produced by special piezoelectric transmitters, bats during navigation, and medical ultrasound scanners.

(b) Practical Applications of Ultrasound

\nUltrasound waves high frequencies allow them to travel along well-defined paths even around obstacles. Key applications include:

1. Cleaning Hard-to-Reach Components:

   • Industrial parts with complex shapes, spiral tubes, or electronic components are placed in a cleaning solution.
   • High-frequency ultrasonic waves are passed through the liquid, causing dust, grease, and dirt particles to detach and fall off completely.

2. Detection of Flaws and Cracks in Metal Blocks:

   • Ultrasound waves are passed through metal structures (used in bridges, buildings, and machinery).
   • Detectors on the opposite side receive the transmitted waves. If a crack or void exists internally, the ultrasound is reflected back, revealing the location of the defect.

3. Medical Imaging (Ultrasonography and Echocardiography):

   • Ultrasonography: Used to obtain images of internal organs such as the liver, kidneys, and uterus. It aids in detecting abnormalities like gallstones or tumors and monitoring fetal growth during pregnancy.
   • Echocardiography: Ultrasonic waves reflect from various parts of the heart to form images of the heart structure and monitor cardiac activity.

4. Medical Treatment (Breaking Kidney Stones):

   • High-intensity ultrasonic pulses are directed targeted at kidney stones inside the patient's body.
   • The ultrasound breaks these stones into fine grains, which are subsequently flushed out of the body through urine.