Application based questions on sound

Contents

  1. Sound CBSE Science Class 8 Chapter Wise Solved Q&A
  2. Class 8 Important Questions for Science – Sound
  3. Class 8 Important Questions for Science – Sound

How many times does it vibrate in a minute? The two types of mechanical waves are: A wave is a disturbance that travels in a medium due to repeated periodic motion of particles about their mean position,- such that the disturbance is handed over from one particle to the other without the actual motion of the medium. It is a wave in which the particles of the medium vibrate perpendicular to the direction of propagation of the wave.

It is a wave in which the particles of the medium vibrate in the direction of propagation of the wave. The sounds of frequency lower than 20 Hz are called the infrasonics or subsonics. Sounds of frequency higher than 20, Hz are called the ultrasonics. The sound heard after reflection from a rigid obstacle is called an echo. At the compression. Is the amplitude of a wave the same, as the amplitude of the vibrating body producing the wave? What is the range of frequencies assciated with a infra sound?

They have very sensitive hearing equipment, can hear the squeaks ultrasound of bat and know when a bat is flying nearby. If the speed of sound is ms-1, find the time for an echo to be heard. Calculate its frequency. More the amplitude of a wave, more is the loudness produced. Higher the frequency of a wave, more is its pitch and shriller is the sound. The loudness depends on energy per unit area of the wave and on the response of the ear, but intensity depends only on the energy per unit area of the wave and is independent of the response of the ear.

The ceilings of concert halls are curved because sound after reflection from it reaches all the corners of the hall and is audible to each person in the hall. Sound waves between the frequencies 1 to 20 Hz. Sound waves of the frequencies above 20, Hz. Let the distance between the reflecting surface and the source of sound production remains the same.

Do you hear echo sound on a hotter day? If the temperature rises, the speed of sound will increase. This in turn will increase the minimum distance required for hearing an echo. No echo is heard because the distance between the source of sound and reflecting body does not increase. How can it be reduced? Reverberation is the repeated multiple reflections of sound in any big enclosed space.

It can be reduced by covering the ceiling and walls of the enclosed space with some absorbing materials like fibre board, loose woolens etc. The bats produce high pitched ultrasonic waves which are not heard by human beings. The ultrasonic waves on striking the insect send back an echo, which is heard by the bat. As the echo is heard by the bat it hovers on the insect and catches it. The object to be cleaned is put in a tank fitted with ultrasonic vibrator. The tank is filled with water containing detergent.

As the ultrasonic vibrator is switched on the detergent rub against the object at a very high speed and hence cleans it.

The ultrasound waves are allowed to pass through metal block to which detectors are fitted. If there is a small defect in the metal block like an air bubble or a crack, then the ultrasound waves are reflected from such spots. Metal block if defective is indicated by the reflected ultrasonic waves. In small rooms this is not the case, hence echoes are heard. The frequency of the vibrating pendulum does not lie within the audible range 20 Hz to 20, Hz and hence it does not produce audible sound.

The particle takes time t equal to the time period to complete one vibration. Let v be the velocity of the wave, then. Identify the sound wave hiving: Identify the sound wave having: A sound wave travelling in a medium is represented as shown in figure, i Which letter represents the amplitude of the sound wave?

Transverse waves a Particles the medium vibrate at right angles. On what factors do they depend. Characteristics of musical sound are: Find the speed of sound in air. Astronauts need radio transmitter to talk to each other on moon. The sound produced by the musical instrument makes the molecules of air vibrate. These vibrations are carried forward by the other molecules till they reach our ear.


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These then vibrate our eardrum to produce sound. Since sound requires a medium to propagate, therefore, sound cannot travel between astronauts on the moon, hence they use radio transmitters. Air is the commonest material through which sound propagates.

Sound CBSE Science Class 8 Chapter Wise Solved Q&A

When vibrating objects, like prongs of a tuning fork move forward, they push the molecules of the air in front of them. This in turn compresses the air, thus, creating a region of high pressure and high density called compression. This compression in the air travels forward. When the prongs of the tuning fork move backward, they create a region of low pressure in the air, commonly called rarefaction.

This region has low pressure, low density and more volume. As the tuning fork continues to vibrate, the regions of compression in the air alternate with the regions of rarefaction. These regions alternate at the same place. The energy of vibrating tuning fork travels outward. This energy which reaches the ears, makes the eardrums to vibrate and thus we hear sound.

It is the linear distance between two consecutive compressions or two consecutive rarefactions. The number of compressions or rarefactions taken together passing through a point in one second is called frequency. Sound can travels through liquid.


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The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans, it is like a stretched rubber sheet, sound vibrations make the eardrum vibrate. The ear drum sends vibration to the inner ear and from there signal is send to the brain and in this way we are able to hear the sounds around us. The amplitude of a sound wave is the maximum amount by which the instantaneous sound pressure differs from the ambient pressure.

Two cycles of a sine wave showing the amplitude of the pressure variation. The variation of maximum amplitude over time is called the envelope of the sound. Sound waves force the medium particles to vibrate, because of the interaction of the particles present in that medium. The loudness of sound depends upon the amplitude of vibration, when the amplitude of vibration is large sound produced is large and when amplitude of vibration, is low sound produced is feeble. A baby has low amplitude of vibration in their ear drum thus sound produced by baby is low in compare to adults.

If the frequency of vibration is higher the sound has high pitch and if the frequency of vibration is lower the sound has low pitch. Whistle will produce sound with higher pitch. Woman will produce sound with higher pitch. Range of sound between frequencies 20 to 20, Hz is called audible sound as sound between these frequencies is easily audible to human beings. But range of sound less than 20 Hz and more than 20, Hz is called in audible sound as sound below 20 Hz and more than 20, Hz is not audible to human beings.

Yes, dog can hear sounds of frequencies higher than Hz, because of this ability of dog it is being used by police for investigation purposes. The ultra sound equipment used for tracking and investigating many medical problems works at frequencies higher than Hz. Unpleasant and undesirable sounds are called noise. Example sound produced by horns of vehicles, sound coming from construction sites, sound produced by factories machineries etc. Explain noise pollution and its causes.

View Answer Ans: Presence of excessive or unwanted sounds in the environment is called noise pollution, the main causes of noise pollution is the sound made by horns of vehicles, sound coming from construction sites, sound produced by factories machineries etc. In humans, the sound is produced by the voice box or the larynx. Will we be able to hear the sound? Yes, the frying pan will vibrate.

Question19 Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons. No, they cannot talk to each other without using any special device because there is no medium in space and sound needs medium to travel.

Class 8 Important Questions for Science – Sound

Question20 List three sources of noise pollution in your locality. Sources of noise pollution gre. Question 21 We have a stringed musical instrument. In which case would the instrument produce a louder sound? It will create more loud sound in case of string stretched with a greater force because amplitude is greater in this case and loudness depends on the amplitude.

Greater will be the loudness, greater will be the amplitude. Question 22 How is sound produced and how is it transmitted and heard by us?

Class 8 Important Questions for Science – Sound

Sound is produced when any object starts vibrating by any means. These vibrations travel from the source all around the environment through the particles of the environment, thus, it reaches to its destination, i.


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  6. Now, it enters our ear and travels down a canal at the end of which a thin membrane is stretched tightly known as eardrum. The eardrum sends vibrations to inner part of the ear and finally reaches to the brain and we hear the sounds. Question 23 An alarm bell is kept inside a vessel as shown in figure. A person standing close to it can distinctly hear the sound of alarm. Now, if the air inside the vessel is removed completely, how will the loudness of alarm get affected for the same person?

    Initially, the person is able to hear the sound coming from air and water distinctly. But after sometime, when the air is completely removed from the bottle, the sound will pass through the water and not reached to man.