Sound Class 9 Science 20 Important Questions with answer

20 important questions on the chapter “Sound” for Class 9 Science, along with detailed answers:

1. What is sound?

   • Answer: Sound is a type of mechanical wave that propagates through a medium (solid, liquid, or gas) as a vibration of particles. It is produced by vibrating objects and travels through the medium in the form of longitudinal waves.

2. How is sound produced?

   • Answer: Sound is produced when an object vibrates. These vibrations cause the surrounding medium (air, water, etc.) to vibrate as well, creating a series of compressions and rarefactions that propagate as sound waves.

3. What is a medium in the context of sound?

   • Answer: A medium is any substance through which sound waves travel. Common media include air, water, and solids. Sound cannot travel in a vacuum as there are no particles to transmit the vibrations.

4. Define frequency of sound.

   • Answer: The frequency of sound refers to the number of vibrations or cycles per second of a sound wave. It is measured in Hertz (Hz). Higher frequency corresponds to a higher pitch of sound.

5. What is amplitude of sound?

   • Answer: The amplitude of a sound wave is the maximum displacement of the particles from their equilibrium position during the vibration. It is related to the loudness of the sound; greater amplitude means a louder sound.

6. Explain the speed of sound.

   • Answer: The speed of sound is the rate at which sound waves travel through a medium. It varies depending on the medium and its properties such as temperature and density. For example, sound travels faster in solids than in liquids, and faster in liquids than in gases.

7. Why does sound travel faster in solids than in liquids and gases?

   • Answer: Sound travels faster in solids because the particles are more closely packed and can transmit vibrations more quickly. In liquids and gases, the particles are farther apart, which slows down the transmission of sound waves.

8. What is the range of hearing for humans?

   • Answer: The range of hearing for humans typically falls between 20 Hz and 20,000 Hz. Sounds below 20 Hz are called infrasound, and those above 20,000 Hz are called ultrasound.

9. What is an echo?

   • Answer: An echo is the reflection of sound waves off a surface, such as a wall or a mountain, and heard again after a delay. The time delay between the original sound and the echo helps determine the distance of the reflecting surface.

10. How does the Doppler effect affect sound?

    • Answer: The Doppler effect refers to the change in frequency or pitch of a sound as the source moves relative to the observer. When the source approaches, the frequency increases (higher pitch); when it moves away, the frequency decreases (lower pitch).

11. Explain the concept of pitch in sound.

    • Answer: Pitch is the perception of how high or low a sound is, which is directly related to the frequency of the sound wave. Higher frequency sounds have higher pitches, while lower frequency sounds have lower pitches.

12. What factors affect the loudness of sound?

    • Answer: The loudness of sound is affected by the amplitude of the sound wave, the distance from the source, and the medium through which it travels. Larger amplitude and closer proximity generally result in louder sounds.

13. What is the principle of sound reflection?

    • Answer: The principle of sound reflection states that when sound waves hit a surface, they bounce back according to the angle of incidence being equal to the angle of reflection, similar to the reflection of light.

14. What is resonance?

    • Answer: Resonance occurs when a system is driven at its natural frequency, causing it to vibrate with larger amplitudes. This phenomenon can amplify sound in musical instruments or even cause damage in mechanical systems.

15. How do musical instruments produce sound?

    • Answer: Musical instruments produce sound through vibrating strings, air columns, or membranes. The vibrations create sound waves that are amplified by the instrument's body and produce a range of pitches and tones.

16. Why does sound travel slower in colder air?

    • Answer: Sound travels slower in colder air because the density of air increases and the molecules move more slowly, which impedes the speed of sound waves.

17. What is the relationship between sound frequency and wavelength?

    • Answer: The wavelength of sound is inversely proportional to its frequency. Higher frequency sounds have shorter wavelengths, while lower frequency sounds have longer wavelengths. The relationship is given by the formula: $\text{Speed} = \text{Frequency} \times \text{Wavelength}$.

18. How can sound be prevented from traveling through a medium?

    • Answer: Sound can be prevented from traveling through a medium by using soundproof materials or barriers that absorb or block sound waves. Materials like foam, thick curtains, and insulating panels are commonly used for soundproofing.

19. What is the phenomenon of sound refraction?

    • Answer: Sound refraction occurs when sound waves change direction as they pass through different mediums with varying densities. This can cause the sound to bend and change speed, leading to effects like the bending of sound around corners.

20. Explain the significance of sound intensity and decibels.

    • Answer: Sound intensity measures the power per unit area of a sound wave and is usually expressed in watts per square meter (W/m²). The loudness of sound is measured in decibels (dB), a logarithmic scale that quantifies sound intensity. For example, a whisper is around 30 dB, while a rock concert might exceed 120 dB.

These questions cover fundamental concepts and practical aspects of sound, which should help in understanding and studying the chapter effectively.