Chapter-12 Sound NCERT Exampler

1.How does the sound produced by a vibrating object in a medium reach your ear?

Explanation:

The surrounding particles of the medium must also vibrate when an object vibrates. The nearby particles are made to vibrate by the vibrating particles. As a result, until it reaches your ear, the sound made by a vibrating object in a medium is transmitted from particle to particle.


2. Describe how your school bell produces sound.

Explanation:

The school bell moves forward and backward when struck with a hammer, creating vibrations that lead to compression and rarefaction. The school bell makes sound in this manner.


3. Why are sound waves called mechanical waves?

Explanation:

Sound waves must travel through a medium in order to interact with the particles therein. Thus sound waves are also known as mechanical waves.


4. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

Explanation:

No. To spread, sound waves need a medium. I won't be able to hear any sound made by my friend because there isn't an atmosphere on the moon and sound cannot travel in a vacuum.


5. Which wave property determines (a) loudness, (b) pitch?

Explanation:

(a) Amplitude - The relationship between a sound's amplitude and loudness is one of cause and effect. The sound is louder the larger the amplitude.

(b) Frequency - The relationship between a sound's frequency and pitch is straightforward. High pitch indicates high frequency, and vice versa.


6. Guess which sound has a higher pitch: guitar or car horn?

Explanation:

A sound's frequency has a direct correlation with its pitch. As a result, when compared to an automobile horn, the guitar has a higher pitch.


7. What are the wavelength, frequency, time period and amplitude of a sound wave?

Explanation:


a. Wavelength – The distance between two consecutive rarefactions or compressions is referred to as the wavelength. The SI wavelength unit is the metre (m)

b. Frequency – The quantity of oscillations per second is known as frequency. Hertz is the SI unit of frequency (Hz).


c. Amplitude – The highest point that a sound wave’s crest or trough can travel is known as amplitude.


d. Time span – The time span is the amount of time needed to create one full cycle of a sound wave.


8. How are the wavelength and frequency of a sound wave related to its speed?

Explanation:

These are some examples of how wavelength, speed, and frequency are connected:

Wavelength x Frequency = Speed

V = λ v


9. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

Explanation:

Due to that,

Sound waves have a frequency of 220 Hz.

Sound wave velocity is 440 m/s.

Determine the wavelength.

The fact that

Wavelength x Frequency equals speed.

V = λ v

Wavelength 220 = 440

Wavespan = 440/220

Wavelength is two.

Hence, the sound wave’s wavelength is 2 metres.


10. A person is listening to a tone of 500 Hz, sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?

Explanation:

The time period is equal to the time elapsed between each compression from the source, and the time elapsed between each compression is equal to the frequency. Consequently, it can be determined as follows:

T= 1/F

T= 1/500

T = 0.002

Hence, the distance between the reflecting surface and the source is equal to 1026/2, or 513 metres.


11. Distinguish between loudness and intensity of sound.

Explanation:

The intensity of a sound wave is the volume of sound energy that moves across a space each second. Its amplitude determines how loud something is.


12. In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?

Explanation:

When compared to other media, sound moves through solids more quickly. As a result, sound propagates most quickly through iron and least slowly through gas at a given temperature.


13. An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms-1?

Explanation:

(v) = 342 ms-1 is the speed of sound.

Echo returns in 3 seconds (time (t)).

Sound travels for a distance of v t = 342 3 = 1026 m.

Sound must travel twice as far in the allotted time as it does between the source and the reflecting surface


14. What is sound, and how is it produced?

Explanation:

Vibrations cause sound to be created. The neighbouring particles of the medium are made to vibrate when a body vibrates. As a result, the medium is disturbed, causing waves to propagate until they reach the ear. Hence, the sound is created.


15. Draw a diagram to illustrate the process by which air near a sound source is compressed and rarefied.

Explanation:

The school bell moves forward and backward when struck with a hammer, creating vibrations that lead to compression and rarefaction. It exerts great pressure on its surroundings as it moves forward. This area of extreme pressure is referred to as compression. When it moves backward, the area around it experiences low pressure. This region is known as rarefaction.



16. How come a sound wave is referred to as a longitudinal wave?

Explanation:

A form of vibration known as a longitudinal wave travels through a medium parallel to or concurrently with the wave’s direction. The path of the disturbance is parallel to the direction of the particle vibration in the medium. Hence, a sound wave is known as a longitudinal wave.


17. Which characteristics of the sound help you to identify your friend by his voice while sitting with others in a dark room?

Explanation:

The sound quality is a trait that enables us to recognise a specific person's voice. The pitch and loudness of two people may be the same, yet they will have different attributes.


18. What is reverberation? How can it be reduced?

Explanation:

Reverberation is the continual repeated reverberations of sound in a large confined space. Noise can be decreased by using sound-absorbing materials, like loose woollens and fibre boards, to cover the walls and ceilings of enclosed places


19. Does sound follow the same laws of reflection as light does? Explain.

Explanation:

Yes. The same reflectional principles apply to sound as they do to light. At the point of incidence, the incident and reflected sound waves form an equal angle with respect to the surface normal. Moreover, the plane in which the incident sound wave, the normal at the point of incidence, and the reflected sound wave all reside is the same.


20. What is the loudness of sound? What factors does it depend on?

Explanation:

Loud noises have a lot of energy. The amplitude of vibrations directly affects how loud something is. It is proportional to the square of the sound wave's amplitude.


21. Give two practical applications of the reflection of sound waves.

Explanation:

(i)The speed and range of underwater objects are determined by sound reflection. This approach is known as SONAR.

(ii) The stethoscope's operation - The doctor hears the patient's heartbeat through a number of sound reflections.


22. Provide an explanation of how ultrasonography can be used to find flaws in a meta block.

Explanation:

Defects in metal blocks prevent ultrasound from penetrating and bouncing off of them. In order to detect faults in metal building blocks, this technique is used. Construct the configuration shown in the picture by installing detectors on one end of a metal block and running ultrasound through the other. The damaged area of the metal block will not be detected by the detector because it will not allow ultrasound to travel through. This method makes use of ultrasonography to locate faults in metal blocks.


23.  How come a sound wave is referred to as a longitudinal wave?

Explanation:

A form of vibration known as a longitudinal wave travels through a medium parallel to or concurrently with the wave's direction. The path of the disturbance is parallel to the direction of the particle vibration in the medium. Hence, a sound wave is known as a longitudinal wave.


24. How is ultrasound used for cleaning?

Explanation:

Ultrasonic sound waves are used to pass through a cleaning solution as it passes through the objects that need to be cleaned. Ultrasound waves' high frequency aids in separating dirt from items. In this manner, ultrasonography is applied to cleaning.


25. Explain how bats use ultrasound to catch prey.

Explanation:

Ultrasonic squeaks with a high pitch can be produced by bats. These squeaks bounce off of things like prey and come back to their ears. This aids a bat in determining how far away its prey is.