BASIC SCIENCE SOLUTION CLASS 8 CHAPTER 9 Sound

Exercise 

A. Answer the following in not more than 20 words

1. Name the three characteristics that help us distinguish one sound from another. 

2. What does the loudness of a sound depend on?

3. What is the pitch of a sound? What does it depend on?

4. What would happen to the sound produced by a stretched string if you increased its tautness?

5. What determines the pitch of a percussion instrument? 6. What happens to the sound produced when you strike a glass as you increase the level of water

in it?

7. What are infrasonics?

8. Name two animals which can hear sounds that we cannot hear.

9. How do bats use echoes?

B. Answer the following in not more than 40 words. 

1. What are harmonics? Which characteristic of a sound do they determine?

2. What is the basic difference between music and noise? What are regular vibrations? 3. What determines the harmfulness of noise from the point of view of health? Mention two sources

of noise pollution.

4. Why do we see a flash of lightning before we hear the accompanying sound of thunder? Which characteristic of sound determines how far it can travel before dying out?

5. Name the organ which helps us speak. How are sounds produced by it? 

6. What are echoes? Why do we not hear them all the time?

7. How are echoes used in medicine?

C. Answer the following in not more than 100 words.

1. Explain how sound travels through air. Why does sound travel faster through solids than through air?

2. Explain how we hear.

D. Complete the following.

1. The frequency of sound is measured in .......

2. The maximum displacement of a vibrating body from its position of rest is its.....

3. The frequency of ultrasonics is               than the range of human hearing

4. Sound vibrations die out after travelling some distance due to the loss of

5. Sound Sound needs a to travel.

6. Industrial noise can be reduced by proper..... 

7. The reflecting surface has to be at least. ...away for us to hear an echo distinctly.

E. Choose the correct option in each of the following. 

1. What helps us distinguish between the same note of musical instruments?

(a) Pitch

(b) Frequency

(c) Harmonics

(d) Amplitude

2. The frequencies of harmonics are

(a) not related to the frequency of the fundamental

b) constants

(c) multiples of the frequency of the fundamental

(d) less than the frequency of the fundamental

3. Sound travels

(a) the fastest in air

(c) faster in air than in water

(b) the fastest in vacuum

(d) faster in solids than in air

4. The decibel is a unit that measures

(a) loudness

(b) pitch 

(c) frequency

(d) quality

5. Women are more high-pitched than men because their vocal cords

(a) are tauter

(b) are shorter

(c) are thicker

(d) vibrate less

6. The ceilings of theatres are covered with special materials to

(a) increase the reflection of sound

(b) minimise the reflection of sound

(c) increase regular reflection of sound

(d) increase the loudness of sound

Answer

A. 

1. Frequency, amplitude, and quality. 

2. The strength of vibrations or the amplitude of a sound wave. 

3. The highness or lowness of a sound, which depends on its frequency. 

4. The pitch of the sound would increase. 

5. The size and shape of the vibrating object or the instrument's resonant chamber. 

6. The pitch of the sound would increase. 

7. Sound waves with frequencies below the range of human hearing. 

8. Dogs and bats. 

9. Bats emit high-frequency sounds and use the echoes to locate objects.

B. 

1. Harmonics are multiples of the fundamental frequency that determine the timbre or quality of a sound. 

2. Music is a pleasant arrangement of regular vibrations, while noise is unpleasant and irregular vibrations. 

3. The harmfulness of noise depends on its intensity and duration. Sources of noise pollution include traffic and industrial activities. 

4. Light travels faster than sound, so we see lightning before we hear thunder. The characteristic of sound that determines its distance is its intensity or amplitude. 

5. The larynx or voice box helps us speak by producing sound through the vibration of vocal cords. 

6. Echoes are reflected sounds that reach our ears after bouncing off surfaces. We do not hear them all the time because they depend on the presence of reflecting surfaces. 

7. Echoes are used in medicine for imaging techniques like ultrasound to visualize internal organs.

C. 

1. Sound travels through air as a longitudinal wave, where particles vibrate parallel to the direction of wave propagation. It travels faster through solids because the particles are closer together, allowing for faster energy transfer. 

2. We hear when sound waves enter our ears, causing the eardrum to vibrate, which in turn causes tiny hair cells in the cochlea to convert the vibrations into electrical signals that the brain interprets as sound.

D. 

1. Hertz (Hz). 

2. Amplitude. 

3. Higher. 

4. Energy. 

5. Medium. 

6. Noise control measures. 

7. 17 meters.

E. 

1. c) Harmonics. 

2. c) Multiples of the frequency of the fundamental. 

3. d) Faster in solids than in air. 

4. a) Loudness. 

5. b) Are shorter. 

6. b) Minimize the reflection of sound.

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