Reflection of Sound
- The Bouncing Back of sound when it strikes a hard surface is called Reflection of Sound.
- For Example Sound is Reflected when hit by a Surface like wall,Metal sheet,Hard Wood Etc.
- Soft Surfaces reflect less and absorb more sound
- Sound can be reflected from any type of surface whether rough or smooth
- As sound waves are are much longer than light waves The need larger area for reflection
- The Reflection of sound is same as the law of reflection of light
Application of reflection of sound
- Megaphone or Bulb Horn – They are designed such that they can send sound in a particular direction without spreading all around
- They are made funnel shaped so that the sound waves can be reflected repeatedly and waves can go in forward direction
- Due to successive reflection Amplitude of the sound wave adds up so loudness increases
- Stethoscope-Stethoscopes work like speakers for doctors:
- They amplify (make louder) the sounds inside your body to give them a better idea of what’s going on in there!
- On one end are earpieces that go in the doctor’s ears.
- Coming down from the earpieces are hollow tubes that connect at the end to the special piece the doctor places against the patient’s body, known as the “diaphragm” or the “bell.”
- Sound Board
– In big hall sound can be observed by walls,ceilings,floor,seats and even by the clothes of people sitting inside.
– Because of much absorption speech cannot be heard properly inside
_ sound board reflects sound and helps spreading sound evenly in the big hall
Basically Sound board is a concave board placed behind the speaker
– It also works on the concept of multiple reflection of sound
-So in a large hall is also made curved roof so that after reflection sound may reach all the direction
Echo- The repetition of sound caused by reflection of sound waves is called echo.
- Echo is also a reflected sound
- A soft surface trends to absorb sound so there is no echo
Calculation of minimum distance to hear an echo
- It has been estimated by scientists that if two sounds reach our ears with in a n interval of 1/10th of a second we cannot hear those sounds a s separate. it will be heard as same
- The minimum distance from a sound reflective surface (wall etc.) to hear an echo is 17.2 metre.
- this means that to hear an echo of shout we should be at least 17.2 metre away from a sound surface like wall
- The 17.2 metre is applicable for temperature of 200 c .
A simple Problem
A man claps his hand near a mountain and hears its sound after 4 second. if the speed of sound is 330 m/s . calculate the distance between the mountain and Man.
Answer- Here the time taken is 4 second(to reach the mountain and to return)
so, time taken to reach the mountain will be 4/2 = 2 second
We Know Speed =distance/time
Distance= speed * Time
So Distance = 33082 = 660 Meter
Reverberation – The persistence of sound in a big hall due to repeated reflections from the walls ceiling and floor of the wall is called reverberation
Basically it is multiple Echoes.
- A short reverberation is desirable as it gives life to sound and boosts sound level
- but if the reverberation is too long sound becomes distorted and un-comforting to our ears
- To reduce the reverberation sound absorbing materials are sued.
The frequency range of humans
- Our human ear can only hear sound of the range 20 hz to 20000 hz and this range is known as frequency range of humans
- and this range is also called audible range
- The sound waves of frequencies below 20 hz is called infrasonic sound
Infrasonic sound is produced by pendulum,earth quake and few animals.
- Rhinoceroses communicate using infrasonic of frequency as low as 5 Hz.
- Whales and elephants produce sound in the infrasonic range.
- It is observed that some animals get disturbed before earthquakes.
- Earthquakes produce low-frequency infrasonic sound before the main shock waves begin which possibly alert the animals
- The sound waves of frequencies above 20000 hz is called Ultra sonic sound
- Dogs bats cats deer monkey can hear ultra sonic sounds
Applications of UltraSonic Sound
- Ultra sound is used in industries to detect flaws(cracks) in metal blocks
- Metallic components are generally used in construction of big structures
like buildings, bridges, machines and also scientific equipment
- The cracks or holes inside the metal blocks, which are invisible from outside reduces the
strength of the structure.
- Ultrasonic waves are allowed to pass through the metal block and detectors are used to
detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect
- Ultra sound is used to clean hard to reach parts of objects such as spiral tubes,odd shaped machines and electronic components etc.
- Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned.
- Ultrasound is used to investigate the internal organs of the human body such as liver pancreases kidney uterus etc.
Sonar- Sound Navigation and Ranging is an apparatus used to find the depth of the sea to locate the underwater things like shoals of fish ,ship and enemy submarines
Working Principle of Sonar
- It consist of a transmitter(for emitting ultra sonic waves) and receiver (for detecting ultrasonic waves)
- The transmitter sends a pulse of ultrasound towards the bottom of the sea
- when the pulse strikes the bottom it is reflected back and and received by the receiver
- Half of the time is taken as the time to reach the depth of sea
- Remember the speed of ultra sound in water is same as that of ordinary sound
Sound is produced by vibrations .
- When the vibration is more the amplitude is large and produce large sound
- The loudness of sound is a measure of the sound energy reaching the ear peer second
- The loudness of sound depends on the amplitude of sound waves
- The loudness of sound is represented by decibel
- The softest sound a human can hear is 0 db.
- The loudness of sound people talk in quiet is 65 decibel
- We can distinguish a mans voice and women’s voice of the same loudness without seeing them
- A man’s voice has a low pitch and woman has a high pitch
- The pitch of a sound depends on frequency.
- Low frequency means low pitch and high means high pitch
Quality of sound
- The Quality of sound depend upon the shape of the wave form
The Human Ear
- The three parts of the ear anatomy are the outer ear, the middle ear and the inner ear. The inner ear is also called the cochlea. (‘Cochlea’ means ‘snail’ in Latin; the cochlea gets its name from its distinctive coiled up shape.)
- The outer ear consists of the pinna, ear canal and eardrum
- The middle ear consists of the ossicles (malleus, incus, stapes) and ear drum
- The inner ear consists of the cochlea, the auditory (hearing) nerve and the brain
- Sound waves enter the ear canal and make the ear drum vibrate.
- This action moves the tiny chain of bones (ossicles – malleus, incus, stapes) in the middle ear.
- The last bone in this chain ‘knocks’ on the membrane window of the cochlea and makes the fluid in the cochlea move. The fluid movement then triggers a response in the hearing nerve.