NCERT Solutions for Class 8th Science Chapter 5 Sound Questions and answers based on the latest syllabus of CBSE and JKBOSE NCERT Books
Sound
Exercises
1. Choose the correct answer:
(a) Sound can travel through
- (a) gases only
- (b) solids only
- (c) liquids only
- (d) solids, liquids and gases. ✔️
(b) Which of the following voices is likely to have minimum frequency?
- (a) Baby girl
- (b) Baby boy
- (c) A man ✔️
- (d) A woman
2. In the following statements, tick T against those which are true, and F against those which are false:
(a) Sound cannot travel in vacuum. ( T )
(b) The number of oscillations per second of a vibrating object is called its time period. ( F )
(c) If the amplitude of vibration is large, sound is feeble. ( F )
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. ( T )
(e) The lower the frequency of vibration, the higher is the pitch. ( F )
(f) Unwanted or unpleasant sound is termed as music. ( F )
(g) Noise pollution may cause partial hearing impairment. ( T )
3. Fill in the blanks with suitable words:
(a) Time taken by an object to complete one oscillation is called time period.
(b) Loudness is determined by the amplitude of vibration.
(c) The unit of frequency is hertz.
(d) Unwanted sound is called noise.
(e) Shrillness of a sound is determined by the frequency of vibration.
4. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
- Time Period: Time taken for one oscillation = Total time / Number of oscillations = 4 seconds / 40 = 0.1 seconds.
- Frequency: Number of oscillations per second = 1 / Time period = 1 / 0.1 = 10 Hz.
5. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer:
- Time Period: Time taken for one vibration = 1 / Number of vibrations per second = 1 / 500 = 0.002 seconds.
6. Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak: Stretched membrane
(b) Sitar: String
(c) Flute: Air column
7. What is the difference between noise and music? Can music become noise sometimes?
Answer:
- Noise: Unpleasant, irregular, and chaotic sounds.
- Music: Pleasant, regular, and harmonious sounds.
- Music can become noise if it is too loud, disruptive, or unwanted.
8. List sources of noise pollution in your surroundings.
Answer:
- Traffic
- Construction activities
- Loudspeakers
- Industrial activities
- Household appliances
9. Explain in what way noise pollution is harmful to humans.
Answer:
Noise pollution can cause stress, hearing loss, sleep disturbances, cardiovascular issues, reduced productivity, and impaired cognitive functions.
10. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer:
I would suggest buying the house three lanes away from the roadside. It will be quieter, with less noise pollution, ensuring a more peaceful living environment and better health for the family.
11. Sketch larynx and explain its function in your own words.
Answer:
The larynx, or voice box, is located in the throat. It houses the vocal cords, which vibrate to produce sound when air passes through them. It also plays a role in breathing and protecting the trachea against food aspiration.
12. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain?
Answer:
Light travels much faster than sound. When lightning occurs, we see the flash almost immediately. However, the sound of thunder takes longer to reach us because sound waves travel slower than light waves.
Extended Learning — Activities and Projects
- Visit the music room of your school. You may also visit musicians in your locality. Make a list of musical instruments. Note down the parts of these instruments that vibrate to produce sound.
Answer:
- Guitar: Strings
- Drum: Membrane
- Flute: Air column
- Piano: Strings and soundboard
- Violin: Strings
- If you play a musical instrument, bring it to the class and demonstrate how you play it.
Answer: (This is an activity for students to participate in class.)
- Prepare a list of famous Indian musicians and the instruments they play.
Answer:
- Ravi Shankar: Sitar
- Zakir Hussain: Tabla
- L. Subramaniam: Violin
- Hariprasad Chaurasia: Flute
- Shivkumar Sharma: Santoor
- Take a long thread. Place your hands over your ears and get someone to place this thread round your head and hands. Ask her to make the thread taut and hold its ends in one hand. Now ask her to draw her finger and thumb tightly along the thread. Can you hear a rolling sound like that of thunder? Now repeat the activity while another friend stands near both of you. Can he hear any sound?
Answer:
This activity demonstrates how vibrations travel through a medium (thread) to produce sound that can be heard when directly in contact with the medium. The friend standing nearby may not hear the sound as it is conducted through the thread directly to your ears.
