Class 9 Science Exploration Solutions English Medium

NCERT Solutions Class 9 Science Exploration English Medium

Sound Waves: Characteristics and Applications

Topic: Ultrasonic Sound

Chapter 10. Sound Waves: Characteristics and Applications

This section explains ultrasonic sound waves and their practical applications. It also describes the working principle of SONAR, which uses reflected ultrasonic waves to detect underwater objects and measure distances. 

Ultrasonic Sound

Ultrasonic waves are sound waves having frequencies greater than 20,000 Hz. Humans cannot hear these sounds, but many animals such as bats and dolphins can produce and detect them.

Characteristics of Ultrasonic Waves

• Frequency greater than 20 kHz.
• Cannot be heard by humans.
• Travel in straight lines.
• Can be reflected from small objects.
• Carry high energy and are highly directional.

Applications of Ultrasound

• Medical Imaging – Used for ultrasonography to examine internal organs and monitor foetal development.
• Breaking Kidney Stones – High-intensity ultrasound helps break kidney stones into smaller pieces.
• Industrial Testing – Detects cracks and defects in metal blocks and machine parts.
• Cleaning Delicate Objects – Cleans jewellery, watches and electronic components.
• Animal Navigation – Bats and dolphins use ultrasonic waves for navigation and locating prey.

SONAR (Sound Navigation and Ranging)

SONAR is a device that uses ultrasonic waves to detect underwater objects and measure the depth of seas and oceans. It works on the principle of reflection of sound. 

Working of SONAR

1. An ultrasonic pulse is transmitted into water.
2. The pulse travels through water and strikes an underwater object.
3. The reflected wave (echo) returns to the receiver.
4. The time taken for the echo is measured.
5. The distance is calculated using the speed of sound in water.

Formula:

Distance = (Speed × Time) / 2

Applications of SONAR

• Measuring the depth of oceans and seas.
• Locating submarines and underwater rocks.
• Finding schools of fish.
• Underwater navigation.
• Marine exploration and oceanographic research.

Difference Between Audible and Ultrasonic Sound

ATP Education Concept Builder

Remember that ultrasound is simply a sound wave with a frequency above the human hearing range. SONAR works by sending ultrasonic waves and receiving their reflected echoes to determine the position or distance of underwater objects.

ATP Education Exam Booster

• Remember the frequency ranges of infrasonic, audible and ultrasonic sounds.
• Learn the important applications of ultrasound.
• Understand the working principle of SONAR.
• Memorise the SONAR formula: Distance = (Speed × Time) / 2.
• Know that SONAR is based on the reflection of ultrasonic waves.
• CBSE competency-based questions often ask students to explain why ultrasound is preferred for underwater detection and medical imaging.

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