A. Choose the correct option.
1. Sound is produced because of
a. Air molecules
b. Vibrations
c. Water waves
d. Heat
Correct Answer: b. Vibrations
2. The speed of sound in air at 0°C is about
a. 3 m/s
b. 30,000 m/s
c. 330 m/s
d. 1000 m/s
Correct Answer: c. 330 m/s
3. Sound can travel through
a. Solids and liquids
b. Gases and solids
c. Liquid and gases
d. Solids, liquids, and gases
Correct Answer: d. Solids, liquids, and gases
4. Sound waves of frequencies above 20,000 Hz are called ……… waves.
a. Ultrasonic
b. Supersonic
c. Infrasonic
d. Sonic
Correct Answer: a. Ultrasonic
5. In percussion instruments, vibration of ……… produces sound.
a. Air column
b. String
c. Skin or membrane
d. None of these
Correct Answer: c. Skin or membrane
B. Fill in the blanks with the correct words.
- Sound travels through air in the form of compressions and rarefactions.
- Sound needs a medium to travel.
- Sound travels faster in solids as compared to gases.
- We cannot hear sounds of frequency lower than 20 Hz.
- A continuous noise in our environment is called noise pollution.
C. Write T for True or F for False.
- Sound is always audible. F (We cannot hear very low or very high-frequency sounds.)
- Sound travels at the same speed in all media. F (It travels at different speeds in solids, liquids, and gases.)
- Sound travels in the form of waves. T
- The ‘pitch or shrillness’ of a sound is related to its frequency. T
- Noise pollution can produce stress. T
D. Answer the following questions.
1. How can we produce sound? Give three examples.
Sound is produced by vibrating objects.
- Examples: Plucking a stretched rubber band, beating a drum, clapping your hands.
2. Explain how sound is our basic means of communication.
Sound allows us to speak and listen. We use words and language to share ideas, feelings, and information with each other, making it a fundamental tool for communication.
3. How does sound propagate in air?
When an object vibrates, it pushes and pulls the air molecules next to it. This creates areas where molecules are squeezed together (compressions) and areas where they are spread apart (rarefactions). These compressions and rarefactions travel through the air as a sound wave.
4. What are the three important characteristics of sound waves?
The three important characteristics are:
- Amplitude: Related to the loudness of the sound.
- Frequency: Related to the pitch (how high or low the sound is).
- Timbre: The quality of the sound that helps us distinguish between different sources.
5. What is the range of frequencies that human beings can hear?
Human beings can generally hear sounds with frequencies between 20 Hz and 20,000 Hz.
6. How is the amplitude of a sound wave related to the sound we hear?
The amplitude of a sound wave determines its loudness. A sound wave with a larger amplitude is louder, while a sound wave with a smaller amplitude is softer.
7. Name two stringed and two wind instruments.
- Stringed instruments: Guitar, Sitar
- Wind instruments: Flute, Trumpet
8. Why are percussion instruments mainly used for keeping beats?
Percussion instruments, like drums, produce sharp and distinct sounds that are easy to hear. This makes them perfect for marking the rhythm and keeping the tempo or beat in music.
9. What is noise pollution?
Noise pollution is the presence of excessive, unwanted, or disturbing sound in the environment that can be harmful to human and animal health.
10. List three methods by which we can reduce noise pollution.
Three methods to reduce noise pollution are:
- Planting trees along roads and near buildings, as they absorb sound.
- Using silencers in vehicles and machinery.
- Ensuring that homes and buildings have proper soundproofing.