Lakhmir Singh Physics Class 9 Solutions Sound<\/span><\/strong><\/h2>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:185<\/strong><\/span><\/p>\nSolution 1<\/span><\/strong>
\nYes, sound can travel through iron and as well as water.
\nSolution 2<\/span><\/strong>
\nNo, sound cannot travel through vacuum.
\nSolution 3<\/span><\/strong>
\nRadio waves are used to communicate with one another on moon.
\nSolution 4<\/span><\/strong>
\nSolid – table
\nLiquid – water
\nGas – air
\nSolution 5<\/span><\/strong>
\nVacuum
\nSolution 6<\/span><\/strong>
\nFrequency
\nSolution 7<\/span><\/strong>
\nSI unit of frequency is hertz.
\nSolution 8<\/span><\/strong>
\n(a)Longitudinal wave
\n(b)Transverse wave
\nSolution 9<\/span><\/strong>
\nSpeed of sound is more in steel (solid medium) as compared to water (liquid medium).
\nSolution 10<\/span><\/strong>
\nSound travels faster in iron (being a solid medium).
\nSolution 11<\/span><\/strong>
\nSound travels fastest in steel (solid medium).
\nSolution 12<\/span><\/strong>
\n(a)Sound travels slowest in gases.
\n(b)Sound travels fastest in solids.
\nSolution 13<\/span><\/strong>
\n(a) Speed of sound in copper = 3750m\/s
\n(b) Speed of sound in aluminium = 5100m\/s
\nSolution 14<\/span><\/strong>
\nIt is more convenient to put the ear to the track to hear a train approaching from far away because sound travels faster in solids than in air.
\nSolution 15<\/span><\/strong>
\nSpeed of sound (at 20o<\/sup>C) in:
\n(a) Air = 344 m\/s
\n(b) Water =1498 m\/s
\n(c) Iron =5130 m\/s
\nSolution 16<\/span><\/strong>
\nSupersonic aircrafts
\nSolution 17<\/span><\/strong>
\nSupersonic Speed
\nSolution 18<\/span><\/strong>
\nSupersonic speed refers to the speed of an object which is greater than the speed of sound.
\nSolution 19<\/span><\/strong>
\nIt is common observation that in the rainy season, the flash of lightning is seen first and the sound of thunder is heard a little later. That’s because, speed of
\nlight is very high as compared to speed of sound in air.
\nSolution 20<\/span><\/strong>
\nTransverse and Longitudinal waves.
\nSolution 21<\/span><\/strong>
\nTransverse (water) waves.
\nSolution 22<\/span><\/strong>
\nLongitudinal (sound) waves.
\nSolution 23<\/span><\/strong>
\n(a) Longitudinal waves
\n(b) Transverse waves.
\nSolution 24<\/span><\/strong>
\n(a) Longitudinal waves
\n(b) Transverse waves
\nSolution 25<\/span><\/strong>
\nTransverse waves
\nSolution 26<\/span><\/strong>
\nAn object should vibrate in order to produce sound.
\nSolution 27<\/span><\/strong>
\nVocal cords vibrate in our voice box when we talk.
\nSolution 28<\/span><\/strong>
\nTuning fork is used to produce sound in laboratory experiments.
\nSolution 29<\/span><\/strong>
\nThe sound waves in air are longitudinal waves.
\nSolution 30<\/span><\/strong>
\nThe conclusion from the observation is that the prongs of tuning fork are vibrating, and the vibrating prongs carry energy which gets transmitted to surrounding medium.<\/p>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:186<\/strong><\/span><\/p>\nSolution 31<\/span><\/strong>
\nFalse
\nSolution 32<\/span><\/strong>
\nSlowest: Sound
\nFastest: light
\nSolution 33<\/span><\/strong>
\nSupersonic is used to denote a speed greater than the speed of sound.
\nSolution 34<\/span><\/strong>
\nSound travels faster in hydrogen ( speed of sound in hydrogen is 1284m\/s)
\nSolution 35<\/span><\/strong>
\nThe number 256 on tuning fork signifies the frequency of tuning fork.
\nSolution 36<\/span><\/strong>
\n
\nSolution 37<\/span><\/strong>
\n
\nSolution 38<\/span><\/strong>
\nVelocity of sound = Frequency x wavelength
\nSpeed of sound in air is constant.
\nHence, frequency x wavelength = constant
\nIf frequency is doubled, wavelength is reduced to half.
\nSolution 39<\/span><\/strong>
\nThe frequency in hertz is equal to the number of waves produced per second. In this case, 20 waves are produced per second, so the frequency of sound waves is 20 hertz.
\nSolution 40<\/span><\/strong>
\n(a) Vibrations
\n(b)Compressions; lower; rarefactions
\n(c)Hertz; wavelength; metres
\n(d) Vacuum
\n(e)Greater
\n(f) Decreases
\nSolution 41<\/span><\/strong>
\nVacuum means empty space, region with no matter particles. Sound cannot travel through vacuum because vacuum has no molecules which can vibrate and carry sound waves.
\nSolution 42<\/span><\/strong>
\nThe maximum displacement of the particles of the medium from their original undisturbed positions, when a wave passes through the medium, is called amplitude (A) of the wave.
\n
\nSolution 43<\/span><\/strong>
\n(a) A wave in which the particles of the medium vibrate back and forth in the ‘same direction’, in which the wave is moving, is called a longitudinal wave. These
\nwaves can be produced in all the three media: solids, liquids and gases. A wave in which the particles of the medium vibrate up and down, ‘at right angles’
\nto the direction in which the wave is moving, is called a transverse wave. It can be produced in solids and liquids but not in gases.
\n(b) Sound is a longitudinal wave.
\nSolution 44<\/span><\/strong>
\nDue to the very high speed of light we see the ball hitting the bat first. And it is due to comparatively lower speed of sound that the sound of hitting is heard a little later.
\nSolution 45<\/span><\/strong>
\nLight travels much faster than sound. Due to this, the flash of lightning is seen first and the sound of thunder is heard a little later.
\nSolution 46<\/span><\/strong>
\nLight travels much faster than sound. Due to this, the flash of gun shot is seen first and the sound of gun shot is heard a little later.
\nSolution 47<\/span><\/strong>
\nSound waves in air: Longitudinal, Compression, Rarefaction
\nWater waves: Transverse, Crest, Trough
\nSolution 48<\/span><\/strong>
\n(a) Sound can be produced by the following methods:
\n(i) By vibrating strings (as in a sitar),
\n(ii) By vibrating air (as in a flute),
\n(iii) By vibrating membranes (as in a drum)
\n(iv) By vibrating plates (as in cymbals)
\n(b) Speed of sound wave= frequency x wavelength
\n
\nSolution 49<\/span><\/strong>
\nThis is due to the fact that when the ringing bell is held tightly with our hand, it stops vibrating and the sound coming from it also stops.
\nSolution 50<\/span><\/strong>
\nSound is produced by the following objects:
\n(i) Vibrating stretched strings of sitar
\n(ii) Vibrating stretched membranes of tabla
\n(iii) Vibrating prongs of a tuning fork
\n(iv) Vibrating wings of mosquito
\n(v) Vibrating air columns in flute.
\nSolution 51<\/span><\/strong>
\nIn most of the cases, a sound producing object vibrates so fast that we cannot see its vibrations with our eyes. The time inetrval between two successive vibration is lower than the persistence of vision. Hence we see the object in static state and not in vibration mode.
\nSolution 52<\/span><\/strong>
\nFill water in a beaker up to its brim. Touch the surface of water with the prongs of a sound making tuning fork (which has been struck on a hard rubber pad). The prongs of tuning fork producing sound splash water. This shows that the prongs of a sound producing tuning fork are vibrating (moving forwards and backwards rapidly).
\n
\nSolution 53<\/span><\/strong>
\nThe sound of a gas travels through the vibrations of air layers so it reaches first, but the smell of gas reaches the person through the actual movement of the air
\nlayers, which takes more time.
\nSolution 54<\/span><\/strong>
\nFrequency is number of vibrations produced per second i.e. 128 Hz.
\n
\nSolution 55<\/span><\/strong>
\nVelocity of wave= 340m\/s
\nFrequency= 512 Hz
\nWavelength=?
\nSpeed of sound wave=
\nfrequency x wavelength
\n
\nSolution 56<\/span><\/strong>
\nThe number of complete waves (or cycles) produced in one second is called frequency of the wave.
\nThe time required to produce one complete wave (or cycle) is called time-period of the wave.
\nThe time taken to complete one vibration is called time-period.
\nRelation between time-period and frequency of a wave is:
\n
\nSolution 57<\/span><\/strong>
\nA ringing bell suspended in a vacuum chamber cannot be heard outside because sound cannot travel through vacuum as it has no molecules which can vibrate and carry
\nsound waves.
\nSolution 58<\/span><\/strong>
\nFrequency, f=1020Hz
\nVelocity, v=340m\/s
\nWavelength =?
\nSpeed of sound wave= frequency x wavelength
\n
\nSolution 59<\/span><\/strong>
\nA compression is that part of a longitudinal wave in which the particles of the medium are closer to one another than they normally are, and there is a momentary reduction in volume of the medium. It is a region of high pressure.
\nA rarefaction is that part of a longitudinal wave in which the particles of the medium are farther apart than normal, and there is a momentary increase in the volume of the medium. It is a region of low pressure.
\n<\/p>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:187<\/strong><\/span><\/p>\nSolution 60<\/span><\/strong>
\n(a) Sound is that form of energy which makes us hear. Sound waves are longitudinal waves in air.
\n(b) Sound cannot travel through vacuum. This can be shown by the following experiment:
\n(i) A ringing electric bell is placed inside an air tight glass jar containing air. We can hear the sound of ringing bell clearly. Thus, when air is present as medium in the bell jar, sound can travel through it and reach our ears.
\n(ii) The bell jar containing ringing bell is placed over the plate of a vacuum pump. Air is gradually removed from the bell jar by switching on the vacuum pump. As more and more air is removed from the bell jar, the sound of ringing bell becomes fainter and fainter. And when all the air is removed from the bell jar, no sound can be heard at all. Thus, when vacuum is created in the bell jar, then the sound of ringing bell placed inside it cannot be heard.
\nThis shows that sound cannot travel through vacuum.
\n
\nSolution 61<\/span><\/strong>
\n(a) Sound is produced when an object vibrates. For example, the sound of our voice is produced by the vibrations of two vocal cords in our throat caused by air coming from the lungs.
\n(b) When an object vibrates (and makes sound), then the air layers around it also start vibrating in exactly the same way and carry sound waves from the sound producing object to our ears.
\nSuppose a tuning fork is vibrating and producing sound waves in air. Since the prongs of the tuning fork are vibrating, the individual layers of air are also vibrating. Sound travels in the form of longitudinal waves in which the back and forth vibrations of the air layers are in the same direction as the movement of sound wave.
\n
\nSolution 62<\/span><\/strong>
\n(a) If the air is gradually pumped out of the glass vessel, no sound of the electric bell can be heard because vacuum is created in the vessel and there are no air molecules to carry sound vibrations.
\n(b) Sound cannot be heard on the surface of moon because there is no air on the moon to carry the sound waves.
\nAstronauts talk to one another on the surface of moon through wireless sets using radio waves. This is because radio waves can travel even through vacuum though sound waves cannot travel through vacuum.
\nSolution 63<\/span><\/strong>
\n(a) The number of vibrations per second is called frequency.
\nThe minimum distance in which a sound wave repeats itself is called its wavelength.
\nThe distance travelled by a wave in one second is called velocity of wave.
\nRelation between velocity, frequency and wavelength of a wave:
\nVelocity of wave= frequency x wavelength
\n
\nSolution 64<\/span><\/strong>
\n(a) A wave in which the particles of the medium vibrate back and forth in the ‘same direction’, in which the wave is moving, is called a longitudinal wave. These waves can be produced in all the three media: solids, liquids and gases.
\n
\n(b) Longitudinal waves:
\n(i) The waves which travel along a spring when it is pushed and pulled at one end.
\n(ii) Sound waves in air Transverse waves:
\n(i) The waves produced by moving one end of a long spring up and down rapidly, while other end is fixed.
\n(ii) The water waves or ripples formed on the surface of water in a pond.
\nSolution 65<\/span><\/strong>
\n(a) A compression is that part of a longitudinal wave in which the particles of the medium are closer to one another than they normally are, and there is a momentary reduction in volume of the medium.
\nA rarefaction is that part of a longitudinal wave in which the particles of the medium are farther apart than normal, and there is a momentary increase in the volume of the medium.
\nLongitudinal waves consist of compressions and rarefactions.
\n
\nSolution 66<\/span><\/strong>
\n(a) The ‘elevation’ or ‘hump’ in a transverse wave is called crest. It is that part of the transverse wave which is above the line of zero disturbance of the medium. The ‘depression’ or ‘hollow’ in a transverse wave is called trough. It is that part of the transverse wave which is below the line of zero disturbance of medium. A ransverse wave consists of crests and troughs.
\n(b) Speed of sound= 332m\/s
\nTime =3 sec
\n
\nSolution 67<\/span><\/strong>
\n(a) When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. This is due to the fact that sound travels much more fast through the railway line made of steel than through air.
\n(b) There is no actual movement of air from the sound-producing body to our ear. The air layers only vibrate back and forth, and transfer the sound energy from one layer to the next layer till it reaches our ear.
\nThis will be clear from an example: If we turn on a gas tap for a few seconds, a person standing a few metres away will hear the sound of escaping gas first and the smell of gas reaches him afterwards. The sound of gas travels through the vibrations of air layers so it reaches first, but the smell of gas reaches the person through the actual movement of the air layers, which takes more time. So, it is clear that the sound is not being transmitted by the actual movement of air from the gas tap to person, otherwise he would hear and smell the gas at the same time.<\/p>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:188<\/strong><\/span><\/p>\nSolution 81<\/span><\/strong>
\n
\nSolution 82<\/span><\/strong>
\n(a) Given that there are four complete waves.
\n
\n(b) Frequency = vibrations per sec x number of complete waves
\n= 30 x 4 =120 Hz
\n(c ) Speed = frequency x wavelength
\n= 120 x 0.05= 6m\/s
\nSolution 83<\/span><\/strong>
\nSound can travel through all the given materials.
\nSolution 84<\/span><\/strong>
\n(a) Z medium has no fixed shape and no fixed volume.
\n(b) W medium has a fixed volume but no fixed shape.
\n(c) Y medium has the same composition as that on the moon.
\n(d) X medium has a fixed shape and a fixed volume.
\nSolution 85<\/span><\/strong>
\n(i) The distance between two consecutive compressions or rarefactions is equal to its
\nwavelength. Hence,
\nwavelength is =20 cm= 0.20 m
\n(ii) Speed of wave =4 m\/s
\nWavelength=0.20 m
\nSpeed of wave =frequency x wavelength
\n4 m\/s = frequency x 0.20 m
\nFrequency
\n<\/p>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:206<\/strong><\/span><\/p>\nSolution 1<\/span><\/strong>
\nThe reflection of sound leads to formation of echoes
\nSolution 2<\/span><\/strong>
\nEcho is repetition of sound caused by the reflection of sound waves.
\nSolution 3<\/span><\/strong>
\nThe persistence or sound in a big hall or auditorium is called reverberation.
\nSolution 4<\/span><\/strong>
\na) Megaphone and bulb horn
\nb) Stethoscope
\nc) Soundboard
\nSolution 5<\/span><\/strong>
\nMegaphone
\nSolution 6<\/span><\/strong>
\na) Loudness
\nb) Pitch
\nc) Timbre or Quality
\nSolution 7<\/span><\/strong>
\nThe loudness of sound is measured in decibel. Its symbol is dB.
\nSolution 8<\/span><\/strong>
\nPitch helps us to distinguish between a man’s voice and a woman’s voice, even without seeing them.
\nSolution 9<\/span><\/strong>
\nPitch of a sound is directly proportional to frequency. Higher the frequency, higher is the pitch of the sound.
\nSolution 10<\/span><\/strong>
\n(i) Loudness
\n(ii) Pitch
\n(iii) Timbre
\nSolution 11<\/span><\/strong>
\nQuality or timbre
\nSolution 12<\/span><\/strong>
\nEars enable us to hear sounds.
\nSolution 13<\/span><\/strong>
\nEar drum starts vibrating when outside sound falls on it.
\nSolution 14<\/span><\/strong>
\nThere are three small bones in the middle ear- anvil, hammer and stirrup.
\nSolution 15<\/span><\/strong>
\na) Hammer
\nb) Stirrup
\nSolution 16<\/span><\/strong>
\nThe function of three tiny bones in the ear is to increase the strength of vibrations coming from the ear drum before passing them onto the inner ear.<\/p>\nLakhmir Singh Chemistry Class 10 Solutions <\/strong>Page No:207<\/strong><\/span><\/p>\nSolution 17<\/span><\/strong>
\nEustachian tube
\nSolution 18<\/span><\/strong>
\nAuditory nerve
\nSolution 19<\/span><\/strong>
\nEar canal
\nSolution 20<\/span><\/strong>
\nWe should not put a pin or pencil or any other sharp pointed objects in our ears because they can damage the ear-drum and damaging of ear drum can make us deaf.
\nSolution 21<\/span><\/strong>
\nUltrasound scans are used to monitor the growth of developing baby in the uterus of the mother.
\nSolution 22<\/span><\/strong>
\nAn ultrasound scan for fetus is better than X-rays because X-rays can damage the delicate body cells of the fetus.
\nSolution 23<\/span><\/strong>
\nSONAR is used to find the depth of sea by using ultrasonic sound waves.
\nSolution 24<\/span><\/strong>
\nSO und Navigation And Ranging
\nSolution 25<\/span><\/strong>
\nSoundboard works on the principle of reflection of sound.
\nSolution 26<\/span><\/strong>
\nA megaphone is used to address a small gathering of people.
\nSolution 27<\/span><\/strong>
\nA stethoscope, based on the principle of reflection of sound, is used by doctors to listen to our heartbeats.
\nSolution 28<\/span><\/strong>
\nSoundboard is a concave board which is kept behind the speaker on the stage of a big hall.
\nSolution 29<\/span><\/strong>
\nCurtains and carpets can make our big room less echoey.
\nSolution 30<\/span><\/strong>
\nNo we cannot hear infrasonic waves and ultrasonic waves. That’s because the frequencies of both these waves fall beyond the human audible range of frequencies.
\nSolution 31<\/span><\/strong>
\nInfrasonic sound
\nSolution 32<\/span><\/strong>
\nUltrasonic sounds
\nSolution 33<\/span><\/strong>
\nInfrasonic sound waves
\nSolution 34<\/span><\/strong>
\nAs the frequency increases the pitch of the sound also increases.
\nSolution 35<\/span><\/strong>
\nThe loudness decreases with the decrease in the amplitude of sound.
\nSolution 36<\/span><\/strong>
\nUltrasonic sound waves
\nSolution 37<\/span><\/strong>
\na) reflected
\nb) frequency
\nc) amplitude
\nd) waveform
\ne) reflection
\n