Chapter 9. SOUND

Exercises

1. Choose the correct answer.
Sound can travel through
(a) gases only (b) solids only
(c) liquids only (d) solids, liquids and gases.

Answer : (d) solids, liquids, and gases.

2. Voice of which of the following is likely to have minimum frequency?
(a) Baby girl (b) Baby boy
(c) A man (d) A woman

Answer : (c) A man.

[Generally, adult males tend to have lower-pitched voices compared to females and children, resulting in a lower frequency of vocal vibrations.]

3. 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/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)

Answer :  (a) Sound cannot travel in a 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)

4. Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) Shrillness of a sound is determined by the __________ of vibration.

Answer :  (a) Time taken by an object to complete one oscillation is called period.

(b) Loudness is determined by the amplitude of vibration.

(c) The unit of frequency is hertz (Hz).

(d) Unwanted sound is called noise.

(e) Shrillness of a sound is determined by the frequency of vibration.

5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Answer :  The time period of a pendulum is the time taken for one complete oscillation.

Time period

Time period 

The frequency of a pendulum is the number of oscillations per second.

Frequency

Therefore, the time period of the pendulum is 0.1 seconds and its frequency is 10 Hz.

6. 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 : Here, Frequency = 500 Hz .

Time period Seconds

So, the time period of the vibration of the mosquito's wings is 0.002 seconds.

7. Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak (b) Sitar (c) Flute

Answer : (a) Dholak: The membranes or heads on the top and bottom of the dholak vibrate to produce sound.

(b) Sitar: The strings of the sitar vibrate to produce sound.

(c) Flute: The air column inside the flute vibrates to produce sound.

8. What is the difference between noise and music? Can music become noise sometimes?

Answer : The difference between noise and music are :

Noise	Music
(i) Irregular and random sounds	(i) Structured and intentional arrangement of sounds
(ii)Lacks a specific pattern or melody	(ii) Has melody, rhythm, and harmony
(iii) Often loud and unpleasant	(iii) Pleasing to the ear
(iv) Disruptive and interferes with other sounds	(iv) Can evoke emotions and tell stories
(v) Examples: car horn, construction site, static	(v) Examples: songs, symphonies, rhythmic beats

Some time music can become noise if it becomes disorganized or disruptive.

9. List sources of noise pollution in your surroundings.

Answer : The list sources of noise pollution in our surroundings are :

(i) sounds of vehicles, air craft engines ..etc ,

(ii) explosions including bursting of crackers,

(iii) machines, loudspeakers etc.

(iv) Television and transistor radio at high volumes,

(v) Some kitchen appliances,         

(vi) desert coolers and air conditioners.... etc.

10. Explain in what way noise pollution is harmful to human.

Answer : Some simple ways in which noise pollution can be harmful :

Hearing damage: Loud and prolonged exposure to noise can damage our hearing. It can lead to hearing loss or other hearing-related problems.

Sleep disturbance: Noise can disrupt our sleep patterns, making it difficult to fall asleep or stay asleep. This can result in fatigue, decreased concentration, and irritability.

Stress and anxiety: Continuous exposure to high levels of noise can cause stress and anxiety. It can make us feel on edge, restless, and unable to relax.

Interference with communication: Excessive noise can make it challenging to communicate effectively. It becomes difficult to hear and understand conversations, which can lead to misunderstandings and frustration.

Health issues: Noise pollution has been associated with various health problems such as increased blood pressure, heart disease, and even cognitive impairment.

11. 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 that my parents buy the house three lanes away from the roadside. This is because being away from the roadside will help reduce the harmful effects of noise pollution. Living closer to the roadside means there will be more traffic noise, which can be loud and disturbing. By choosing a house three lanes away, there will be more distance between the house and the noise, creating a quieter and more peaceful living environment.

12. Sketch larynx and explain its function in your own words.

Answer : Photo

The larynx, also known as the voice box, is a part of our throat. It is located at the top of our windpipe (trachea). The main function of the larynx is to produce sound and help us speak.

The larynx contains vocal cords, which are two small bands of tissue. When we breathe in, the vocal cords stay open, allowing air to pass through easily. But when we want to make sound, the vocal cords close up, and when we exhale (breathe out) air, it causes the vocal cords to vibrate. These vibrations create sound waves, which produce our voice.

The larynx, also known as the voice box, is a part of our throat. It is located at the top of our windpipe (trachea). The main function of the larynx is to produce sound and help us speak.

The larynx contains vocal cords, which are two small bands of tissue. When we breathe in, the vocal cords stay open, allowing air to pass through easily. But when we want to make sound, the vocal cords close up, and when we exhale (breathe out) air, it causes the vocal cords to vibrate. These vibrations create sound waves, which produce our voice.

13. 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 why?

Answer : Yes, I can explain why lightning is seen earlier than thunder is heard. The speed of light is much faster than the speed of sound. When lightning occurs, the light reaches our eyes almost instantly, while the sound of thunder takes longer to travel to our ears, resulting in a delay between the two events.