Nature of SoundSound waves are produced by longitudinal vibrations ofmolecules in gases and other media.This means that as a wave travels through a medium, themolecules of the medium oscillate to and fro.The energy of this vibration is carried by the involvedwaves, which is brought to our brains for interpretationas sound.Sound waves that travel in aircome in contact with oureardrums causing it tovibrate.
Can sound waves travel insolid?Can sound waves travel inliquid?If yes give some situations orexamples.
Transmission of Sound WavesThe capacity of matter to transmit sound dependsupon its elasticity.Elastic solid transmit sound well.Inelastic solid like cloth, rubber, plastic andsponge transmit sound poorly
Liquids, in general, are better conductors ofsound than gases.
Solid is considered as the best soundtransmitter.
Why is solid a better sound transmitter thanliquid and gas?
Waves are transmitted fromone place to another by thevibration of particles of themedium.We know that particles in asolid are closer to each otherthan the particles in liquidand in gas.Therefore, sound waves aretransmitted faster and moreefficiently in solid than inliquid and in gas.
The Velocity of Sound Thunder is heard few second after the flask of lightning.An observer standing at a distance from a gun willsee the flash of light before hearing the sound ofthe gunshot
An observer standing at a distance from a fireworks display will see the flash of beautiful lights before hearing the sound of fireworks explosions.These show that sound travels slower thanlight.
The velocity of sound varies in differentmedia.It depends on the elasticity and density ofthe medium.In general, the more elastic the medium, thefaster the sound can travel.The sound can travel faster in a solidmedium than in liquid or gas because theelasticity of solid is greater than that ofliquid and gases.
Assignment:1. Why sound not transmitted in a vacuum?2. A distant lightning can be seen several seconds before the accompanying thunder is heard. Why?
Properties of Sound Waves1. Intensity and Loudness The quantitative description of the intensity of sound is determined by a sound level scale called the decibel scale. Sound intensity is the amount of sound energy flowing each second through a unit area perpendicular to the direction of propagation.
2. Reflection of Sound Waves A sound is reflected when it strikes another body. The reflected wave is called an echo. The reflecting surface has to be at least 17 meters away from the source in order for the echo to be distinct from the original sound. If the reflecting surface is less 17 meters, the reflected sound wave just blends with and strengthens the original sound.
The reflection of sound wave is used indetermining ocean depths and the altitude of anairplane. A sound wave is sent out from a ship toward the sea floor. A wave is reflected from the bottom of the sea and the reflected wave is detected by a receiving device. Using the recorded elapsed time and velocity of sound in water, the ocean depth may be computed.
The airplane altitude, a sonic altimeter is used.Sonic Altimeter is consists of a sound emitter anda record that measures the time interval betweenthe emission of sound and reception of the echo.The product of the time interval and speed ofsound in air at a given temperature divided by 2 isthe plane’s altitude.
Reflected waves can also causeinconvenience to listeners.Echoes from smooth curved walls or ceilingcan increase the intensity of sound in certainparts of the room.In some cases the problem is due toreverberation (repeated echoes).
2. Refraction of Sound Waves Like all types of waves, sound also undergoes refraction when a change in medium or change in property of medium takes place.
On a clear sunny day, the earth’s surface is hot. This causes the temperature of the air just above the surface of the earth to rise.The temperature of the lower layer of air is higher than thelayers above, hence sound should be traveling faster nearthe surface of the earth.This difference in the speed causes the refraction of soundwaves away from the surface.
On a clear night the layer of air nearer the earth’s surface gets cold faster; hence, the lower layer of air is colder.As a result, sound travels faster at the higher layerthan at the lower layer and is refracted toward theearth’s surface.
The sound traveling with air in the same direction is bent toward the earth’s surface.The sound traveling againstthe moving air is bent awayfrom the earth’s surface.
Questions:1. What is an echo?2. When an echo considered useful?3. What happened to the sound waves when they pass from one medium to another of different density?4. Why do sound waves bend a. away from the surface of the earth during daytime b. toward the earth’s surface during nighttime?5. Differentiate intensity from loudness.
Kinds of Sound Waves1. Audible Sound Waves Sound waves that can be detected by human ear. A sound waves with frequencies in the range of 20 to 20,000 Hz can be detected by human ear. This range varies from one individual to another.
2. Ultrasonic Waves Sound waves with a frequencies above 20,000Hz are called ultrasonic waves. These waves can also reach human ear but are not detected. This ultrasonic sound can be detected by some animals Dogs can hear sounds as high as 50,000 Hz, while bats can hear as high as 100,000 Hz
Ultrasonic Waves in the field of MedicineUltrasonic waves are used toprobe human organs instead ofX-rays.Unlike X-rays, ultrasonicwaves does not damage humantissue.
3. Infrasonic Waves Sound waves with frequencies below 20 Hz. Common source of this waves are vibrating heavy machines, earthquake, thunder, and volcanic eruption. These waves are audible but can cause damage to the human body.
How Much Have You Learned?1. Differentiate ultrasonic from infrasonic.2. How is ultrasonic waves utilized in the field of medicine?
Detection of Sound Human and animals have a very sensitive detector of sound – the Ear.The cross-section of human ear is almost similar to thatof other vertebrates.
The ear, which is the peripheral auditory system, isdivided into three parts:
The outer ear called the pinna, collects the sound waves and concentrates them into ear canal to a limited extent. This canal transmits the sound waves to the eardrum.It also protects the eardrum from shock and intrusion byexternal objects.
Air vibration set the eardrummembrane in motion which inturn causes the three littlebones (hammer, anvil, andstirrup) to move.These three little bonesconvert the small amplitudevibrations of the eardrum intolarger-amplitude oscillationsand transfer them to the innerear through the oval window.
Behind this oval window is a snail-shaped, liquid-filled organ called cochlea to where auditory nerves are connected. The larger amplitude oscillations create travelling waves that are transformed into impulses sent to the brain through the auditory nerves.The brain relates and interprets the sound heard tothose previously experienced.
Hearing Damage1. Noise with an intensity level above 120dB isconsidered as an undesirable pollutant in ourenvironment.2. Exposure to loud sounds (80dB or above) for along period can cause temporary hearing loss.3. Overexposure to amplified rock music and noiseproduced by machineries in factories and otherindustrial establishment has been mostly the causeof hearing damage.
4. Our human ear has a built-in muscular control inthe middle ear.This limit the potential damage to the ear caused bysustained loud sound.But our ear cannot react rapidly to protect itselfagainst sudden bursts of short but very loud soundslike gunshots or bomb explosions.If the sound produced is too loud, it can force an earmechanism to go beyond its elastic limit, in thiscase, the hearing damage becomes permanent.
5. Permanent hearing loss may also be caused byphysical damage to ear due to diseases, drugs withside effects, or the natural aging process.6. Infection of the middle ear due to unhygienicpractices can result to hearing damage.7. Hearing damage can also occur to a fetus if thepregnant mother suffered from measles or rubellawithin the first trimester of pregnancy.Rubella can cause malformation of the parts of thefetus’ inner ear.
8. Drugs such as streptomycin have been found tocause permanent hearing loss to small children.Ringing in the ears while the child is undermedication is a symptom of such hearing damage.Because of this, the use of this drug has beencarefully controlled.9. A person may also permanently lose his or hersense of hearing due to normal aging of the auditorysystem.