Chapter 18: SOUND AND COMMUNICATION

Chapter 18: Sound and Communication Class 10 Science and Technology (212) NIOS Textbook Solutions

Chapter 18. SOUND AND COMMUNICATION

INTEXT QUESTIONS 18.1

1. Which sound wave will have its crests farther apart from each other - a wave with frequency 100 or a wave with frequency 500?

Answer: The wave with frequency 100 will have its crests farther apart as its wave length will be higher. For sound waves, the velocity ‘v’ is equal to the product of wavelength and frequency (v = n × λ or

  ) and thus wavelength and frequency are inversely proportional. So for the same velocity, the lower frequency wave will have a larger wave length. Therefore, for the wave with a frequency of 100 Hz, will have a higher wavelength and the crests will be farther apart compared to the wave with frequency 500 Hz.

2. If the velocity of sound is 330 metres per second (m/s), what will be wavelength if the frequency is 1000 Hertz?

Answer:  Here, v=330 m/s , f=1000 Hz

We have,

λ=vf=3301000=33100=0.33 m

Therefore, the wavelength of the sound wave is 0.33 metres (m) (or 33 cm).

3. What is the approximate audible range of frequency for humans?

Answer: The approximate audible range of frequency for humans is 20 Hz to 20,000 Hz (20 kHz).

INTEXT QUESTIONS 18.2

1. Does a wave transfer energy or material?

Answer: A wave transfers energy. Even when the material is displaced, it’s temporary and it comes back to its normal position such as in case of a ripple in water.

2. How do mechanical and electromagnetic waves differ?

Answer:  Difference between Mechanical Waves and Electromagnetic Waves:

Mechanical Waves	Electromagnetic Waves
A medium is essential for propagation. They cannot travel in vacuum.	They can travel through vacuum as well as any medium.
They travel through solids, liquids and gases.	They can travel through empty space and also through matter.
Sound waves travel through liquids and solids with much lower energy losses.	In liquids and solids, electromagnetic waves lose energy very fast.
Their speed is comparatively low. The velocity of sound is highest in solids (a few thousand m/s).	Their speed is extremely high, about 3 lakh km/s (3 × 10⁸ m/s).

3. What is the difference between a transverse and longitudinal wave?

Answer: Difference between Transverse and Longitudinal Waves:

Transverse Wave	Longitudinal Wave
The direction of propagation of the wave (energy transfer) is perpendicular to the direction of oscillation of particles.	Particles of the medium vibrate parallel to the direction of wave propagation.
Particles move up and down while the wave moves forward.	Particles move back and forth in the same direction as the wave.

4. Do transverse waves form in solid?

Answer: Yes. The sound waves travel in solids.

INTEXT QUESTIONS 18.3

1. What is the unit to measure sound intensity?

Answer: The unit to measure sound level is decibel. It’s one tenth of a bel. Actually the decibel is a comparative scale. For us, the reference is fixed at the just audible sound so we normally speak of sound level in decibels.

2. Why do they have many holes at the side of a flute lengthwise ?

Answer: Flute is an organ pipe in which air columns vibrate. More the length of the air column, more the wavelength of sound produced and hence loss the frequency. Holes are provided by the side of the flute so that by closing the holes length of vibrating air column may be changed.

INTEXT QUESTIONS 18.4

1. Give three examples of devices that make use of microphones or speakers or both.

Answer: Three examples of devices that make use of microphones or speakers or both are telephone , radio and television.

2. In a condenser microphone, what will happen if the diaphragm is made very heavy?

Answer: In a condenser microphone, if the diaphragm is made very heavy, the inertia of the diaphragm will be higher. This means it will be difficult for the diaphragm to move rapidly. Its movement can’t be fast enough and so it will not be possible to reproduce very high frequencies.

INTEXT QUESTIONS 18.5

1. List some uses of satellites.

Answer: Satellites are useful in communication, surveying, photographing of geographical features of earth and astronomy.

2. If a satellite equipped with cameras remains fixed at one height above ground even as earth rotates and moves in its orbit, what is its possible use?

Answer: If the satellite is stationary but earth below it keeps moving, the view will keep changing. Thus without the satellite moving, the satellite cameras will see whole surface of earth facing it.

3. Arrange the low orbit, geostationary and polar satellites in decreasing order of altitude above Earth (the highest one comes first).

Answer: The geostationary, polar and low satellites. The geostationary satellites are the highest at about 36,000 km. The Polar satellites are lower than them and the Low Earth Satellites (160-1400 km) are the lowest.

4. Which of the satellites are preferred for communication application?

Answer: Geostationary satellites are preferred for communication application. This is because from earth they appear fixed at the same place. Thus if the antennas are directed towards them once, we don’t have to worry about tracking them.

TERMINAL EXERCISE

1. Fill in the blanks:

(i) Sound travels at a ……………… velocity than light.

(ii) When there is lightning, we first ……………… and then hear it.

(iii) SONAR makes use of ……………… waves while RADAR makes use of ……………… waves.

(iv) Microphone converts sound into ……………… while speaker converts electric signal into ………………

Answer: (i) Sound travels at a lower velocity than light.

(ii) When there is lightning, we first see it and then hear it.

(iii) SONAR makes use of ultrasonic waves while RADAR makes use of electromagnetic waves.

(iv) Microphone converts sound into electric signals while speaker converts electric signal into sound.

2. Multiple choice type questions

(i) Which satellite will see a wider area on Earth?

(a) A low earth orbit satellite (b) A high earth orbit satellite

(c) A medium earth orbit satellite

Answer: (b) A high earth orbit satellite

[ A satellite at a higher orbit is farther from Earth, so it can observe a larger area of the Earth’s surface.]

(ii) India’s first self launched satellite was

(a) IRS (b) Aryabhat (c) Rohini (d) INSAT

Answer: (c) Rohini

[Rohini (RS-1, 1980) was India's first self-launched satellite, as it was placed into orbit by the indigenous SLV-3 rocket.]

(iii) For the same velocity, will a higher frequency of a sound wave mean

(a) Higher wavelength (b) Lower wavelength

(c) The same wavelength

Answer: (b) Lower wavelength.

[ We have, v = f × λ

If the velocity (v) is constant and the frequency (f) increases, then the wavelength (λ) must decrease to keep the product the same. So, higher frequency means lower wavelength.]

(iv) Sound travels fastest in

(a) Solid (b) Liquid (c) Gas

Answer: (a) Solid

[ Sound travels fastest in solids because particles are packed closely together, allowing vibrations to pass more quickly.]

(v) The most suitable medium for RADAR would be

(a) Gas (b) Liquid (c) Solid

Answer: (a) Gas

[ RADAR uses electromagnetic waves (radio waves), which travel efficiently through air (gas) and even through vacuum. Therefore, gas is the most suitable medium.]

3. Why can’t we hear each other on Moon?

Answer: We cannot hear each other on the Moon because sound waves require a material medium (such as air) to travel. The Moon has no atmosphere (vacuum), so sound cannot propagate there. Therefore, we cannot hear each other on the Moon.

4. Describe 2 experiments to show that sound has vibrations associated with it.

Answer: Experiment 1: Using a Tuning Fork

(i) Take a tuning fork and strike it gently on a rubber pad.

(ii) Bring it close to your ear and you can hear a sound.

(iii) Now touch the vibrating tuning fork lightly with your finger.

(iv) You will feel the vibrations and the sound will stop after some time.

Conclusion: This shows that sound is produced due to vibrations.

Experiment 2: Using a Stretched Rubber Band

(i) Stretch a rubber band between your fingers.

(ii) Pluck the rubber band.

(iii) You will observe that the rubber band moves rapidly and produces sound.

(iv) When the vibrations stop, the sound also stops.

Conclusion: This experiment shows that sound is associated with vibrations.

5. What is the relationship between velocity, wavelength and frequency?

Answer: The relationship between velocity (v), wavelength (λ) and frequency (f) is:

 v=f×λ

Where, v = velocity of the wave , f = frequency of the wave  and λ = wavelength of the wave .

6. State 3 differences between sound waves and micro waves.

Answer: The differences between sound waves and microwaves.

Sound Waves	Microwaves
Sound waves are mechanical waves.	Microwaves are electromagnetic waves.
They require a material medium for propagation and cannot travel in vacuum.	They can travel through vacuum as well as a medium.
Their velocity is comparatively low (about 330 m/s in air).	Their velocity is very high (about 3 × 10⁸ m/s).

7. What are the differences between longitudinal and transverse sound waves?

Answer: The differences between longitudinal and transverse Waves:

Longitudinal Waves	Transverse Waves
Particles of the medium vibrate parallel to the direction of wave propagation.	Particles of the medium vibrate perpendicular to the direction of wave propagation.
They consist of compressions and rarefactions.	They consist of crests and troughs.
Example: Sound waves in air.	Example: Light waves and waves on a stretched string.

8. Will sound move faster in solid or air?

Answer: Sound travels faster in solids than in air because particles in solids are closely packed, providing higher elasticity and faster vibration transfer. In air, particles are farther apart, so speed is much lower.

9. What is the basic difference between noise and music ?

Answer: The difference between noise and music:

Noise	Music
Noise is an unpleasant and unwanted sound.	Music is a pleasant and soothing sound.
It is produced by irregular and random vibrations.	It is produced by regular and periodic vibrations.
Noise causes disturbance and discomfort.	Music creates a pleasant hearing experience.

10. What makes your voice appear more musical when you sing in a bathroom?

Answer: A bathroom enhances musicality due to reverberation. Hard surfaces repeatedly reflect sound waves, creating multiple echoes that blend together. This prolongs and enriches the sound, adding depth and resonance, making your voice appear fuller and more musical than in an open, absorbing space.

11. How is active SONAR different from passive SONAR?

Answer: The difference between active SONAR and passive SONAR :

Active SONAR	Passive SONAR
It transmits ultrasonic waves and receives the reflected waves (echoes).	It does not transmit waves; it only receives sounds coming from objects.
It is used to detect and measure the distance and location of objects.	It is used to listen to and identify sounds produced by objects.
Example: Detecting underwater objects and measuring depth.	Example: Detecting submarines by listening to their sound.

12. What are the relative merits of SONAR and RADAR? Why is it better to use SONAR in water?

Answer:

SONAR	RADAR
Uses ultrasonic (sound) waves.	Uses electromagnetic (radio) waves.
Mainly used under water to detect and measure distance of objects.	Mainly used in air and space to detect objects and determine their position.
Sound waves travel efficiently in water with low energy loss.	Electromagnetic waves lose energy more quickly in water.

SONAR is better in water because sound waves can travel through water with much lower losses, while electromagnetic waves are absorbed quickly in water. Therefore, SONAR is more effective for detecting underwater objects and measuring depth.

13. How does SONAR help in estimating the distance of an object?

Answer: SONAR (Sound Navigation and Ranging) works on the echo principle. It transmits an ultrasonic sound pulse from a ship towards the seafloor/object. The pulse reflects back as an echo, which is detected by a receiver. By knowing the speed of sound in water (v) and measuring the time (t) taken for the echo to return, the distance (d) is calculated using the formula: 

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