Class 9 Science Exploration Solutions English Medium

NCERT Solutions Class 9 Science Exploration English Medium

Sound Waves: Characteristics and Applications

Topic: Assignments - What Have You Learned?

Chapter 10. Sound Waves: Characteristics and Applications

This assignment covers all the important concepts of the chapter, including the production and propagation of sound, characteristics of sound waves, speed of sound, reflection of sound, echo, reverberation, ultrasound and SONAR. The questions follow the latest CBSE competency-based assessment pattern. 

1. One Word Answer

1. The form of energy produced by vibrating objects.
2. The type of wave through which sound travels.
3. The region of high pressure in a sound wave.
4. The region of low pressure in a sound wave.
5. The SI unit of frequency.
6. The quantity that determines the loudness of sound.
7. The quantity that determines the pitch of sound.
8. The phenomenon of bouncing back of sound.
9. The device used to detect underwater objects using sound.
10. Sound having a frequency greater than 20,000 Hz.

2. Fill in the Blanks

1. Sound is produced due to __________ of objects.
2. Sound cannot travel through a __________.
3. Sound travels fastest in __________.
4. The SI unit of frequency is __________.
5. The time period of a wave is represented by __________.
6. Echo is produced due to the __________ of sound.
7. Ultrasonic waves have frequencies greater than __________ Hz.
8. SONAR works on the principle of __________ of sound.
9. Loudness depends on the __________ of vibration.
10. Pitch depends on the __________ of vibration.

3. True or False

1. Sound can travel through vacuum.
2. Sound is a longitudinal mechanical wave.
3. Compressions are regions of low pressure.
4. Frequency is measured in hertz.
5. Greater amplitude produces louder sound.
6. Echo and reverberation are the same phenomenon.
7. Ultrasonic waves can be heard by humans.
8. SONAR is mainly used underwater.
9. Sound transfers energy but not matter.
10. Bats use ultrasonic waves for navigation.

4. Match the Following

5. Very Short Answer Questions

1. Define sound.
2. Why is sound called a mechanical wave?
3. Name the two regions of a longitudinal wave.
4. What is wavelength?
5. Define frequency.
6. What is amplitude?
7. State one condition required to hear an echo.
8. What is reverberation?
9. What is ultrasound?
10. Expand the term SONAR.

6. Short Answer Questions

1. Explain how sound is produced.
2. Describe the Bell Jar Experiment and its conclusion.
3. Differentiate between compression and rarefaction.
4. Explain the propagation of sound through a medium.
5. Describe the characteristics of sound waves.
6. Differentiate between loudness and pitch.
7. Explain the factors affecting the speed of sound.
8. State the laws of reflection of sound.
9. Differentiate between echo and reverberation.
10. Explain the working principle of SONAR.

7. Long Answer Questions

1. Describe the production and propagation of sound with suitable diagrams.
2. Explain longitudinal waves with the help of compressions and rarefactions.
3. Describe wavelength, frequency, time period, amplitude and speed of sound.
4. Explain reflection of sound and discuss its applications.
5. Describe echo and reverberation along with their differences.
6. Explain ultrasonic waves and their applications.
7. Describe the construction and working of SONAR.
8. Discuss the importance of sound waves in science, medicine and technology.

8. Case Study Questions

Case Study – 1

A student places an electric bell inside a glass bell jar. As the air is gradually removed from the jar, the ringing sound becomes weaker and finally cannot be heard, although the bell continues to vibrate.

1. What does this experiment prove?
2. Why does the sound disappear?
3. Can sound travel through vacuum?
4. Name the type of wave produced by the bell.

Case Study – 2

A boy shouts loudly near a hill and hears the same sound again after a short interval.

1. Name the phenomenon observed.
2. What causes this phenomenon?
3. State one condition necessary for hearing it.
4. Give one practical application of this phenomenon.

Case Study – 3

A dolphin emits ultrasonic waves while swimming underwater. The reflected waves help it detect nearby objects.

1. Which type of sound is used?
2. Why can't humans hear these waves?
3. Which device works on the same principle?
4. State one more application of ultrasonic waves.

Case Study – 4

A sound wave has a frequency of 500 Hz and a wavelength of 0.68 m.

1. Calculate the speed of the sound wave.
2. Write the formula used.
3. Which characteristic determines the pitch?
4. Which characteristic determines the loudness?

Case Study – 5

An auditorium is fitted with curtains, carpets and cushioned seats.

1. Which sound phenomenon is reduced by these materials?
2. Why is it necessary to reduce this phenomenon?
3. Name two sound-absorbing materials used in auditoriums.
4. How does this improve the quality of sound?

9. Competency-Based Questions

1. Why is vibration necessary for the production of sound?
2. Explain why astronauts cannot hear each other directly in space.
3. Why does sound travel faster in solids than in gases?
4. How does amplitude affect the loudness of sound?
5. Why does frequency determine the pitch of sound?
6. Explain why echo is not heard in a small classroom.
7. How does reverberation affect speech in large halls?
8. Why are ultrasonic waves preferred for medical imaging?
9. How does SONAR help ships navigate safely underwater?
10. Explain how sound transfers energy without transferring matter.

10. HOTS Questions

1. Why is sound classified as a mechanical longitudinal wave?
2. A sound wave travels from air into water. Which properties change and which remain unchanged? Explain.
3. Why is thunder heard after lightning, even though both occur at the same time?
4. How does the design of an auditorium improve the quality of sound?
5. Compare echo and reverberation with suitable real-life examples.
6. Explain why bats can fly safely in complete darkness.
7. How does ultrasound help detect internal defects in metal blocks?
8. A submarine uses SONAR to detect an underwater object. Explain the principle involved.
9. How would communication be affected if sound could travel through vacuum?
10. Prepare a flow chart showing the sequence: Vibration → Sound Wave → Propagation → Reflection → Echo → Ultrasound → SONAR.

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