Sound | Types of Sound | Conditions for Sound Production | How Human produce sound?
Sound
1:- what is sound
2:- Sound waves need a medium
3:- Sound waves travel by compression and rarefaction, direction of sound
4:- Sound produced by haman
5:- Factors affecting the speed of sound
6:- Speed of sound
7:- Types of sound
8:- A few application of ultrasound waves
9:- Sonic boom
10:- Echo
11:- Echolocation
12:- Characteristics of sound
(Loudness, pitch, timbre(quality)
13:- Music and Noise
14:- How sound is detected by Our Ear
1:- Sound :
Sound is a form of energy produced by vibrating objects. Vibration of a particle is a necessary requirement produce sound .
2:- Sound waves need a medium,
sound waves are mechanical waves that need a material medium to propagate. They cannot travel in vacuum. Thus the alarm will not be heard if an alarm clock is put inside a jar and all the air from the jar is removed to create a vacuum. The medium can be liquids, solids and gases.
3:- Sound waves travel by Compression and rarefaction.
• When an object such as a drum is struck, the drumskin moves upwards, it compress the air above it. When the drumskin moves downward, the air molecules spread out, compressing the air next to it.
• Since longitudinal waves are made of compression and rarefactions, therefore, a sound wave is a longitudinal wave caused by vibration and carried through a substance.
• Sound waves travel in all direction from their souce. But, air or other matter does not travel with the sound waves. The particles of air only vibrate back and forth.
4:- Sound produced by Humans
In humans the sound is produced by the voice box or the larynx which is the upper end of the windpipe. Two vocal chords, are stretched across the voice box in such a way that it leaves a narrow slit between them for the passage of air.
When the lungs force air through the slit, the vocal chords vibrate, producing sound.
5:- Factors affecting the Speed of Sound
• The speed of sound varies in different media. Sound travels quickly through air, but it travels faster in liquids and fastest in solids.
Gas ↓ increasing
Liquid ↓ speed of
Solids ↓ sound
• The speed of mechanical waves, the density, elasticity and temperature of the medium affect the Sound's speed increases with elasticity and decreases with density.
• Temperature of the medium also affects the speed of sound:-
The cooler the medium is, the slower the speed of sound. In air for every degree Celsius rise in temperature, velocity of sound in air increases by 0.61 m/s.
It means that if the velocity of sound in air at 0°C is 330 m/s. Then velocity at temperature 25°C would be
330 + 25 × 0.61 = 345.25 m/s. At height of 12000 m above sea level, the temperature of the air is so low that the speed of sound is only 290 m/s.
• Effect of Pressure :- The change in pressure is no effect on the velocity of sound
• Effect of humidity:- Density of humid air is 5/8 times the density of dry air. Therefore, velocity of sound in humid air is more than the velocity in dry air.
6:- The speed of sound
Speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefactions, travels per unit time.
speed of sound = frequency × wavelength
Light travels faster than sound. In thunderstorm, we always see lightning before we hear thunder. The speed of light at 300,000,000 m/s os about one million times faster than the speed of sound in air which is only about 330m/s.
7:- Types of Sound
A human ear can hear only sounds having frequency 20 Hz to 20,000 Hz
This is called audible frequency range.
The sound waves having frequency less than 20Hz are called Infrasonic.
The sound waves having frequency more than 20,000 Hz are called ultrasonic.
Earthquakes, volcanic eruption and some animals like whales and elephants produce infrasonic to communicate. The range of hearing is different for different animals. A dog can hear sound up to frequency 50,000 Hz and a bat up to 1,00,000 Hz. The range of hearing for dolphins seems to be maximum.
Bats produce ultrasonics and can find their path even in pitch dark. Other animals such as dogs, cats, tortoise, birds and insects also produce ultrasonic sounds. Dolphins use ultrasound to find fish and to detect sharks and also to communicate with each other.
8:- A few applications of ultrasound waves:-
Due to very high frequency
(< 20,000Hz), ultrasound waves possess two special properties :
1):- They do not lose much energy while travelling through a medium. Hence, their penetration power is maximum.
2):- Normally, these waves do not undergo bending. Because of the above properties, they are used.
a)- In place of X-ray to take pictures inside of a human body
This is called ultrasonography.
It is considered to be safe and less harmful to human tissues than X-rays. Ultrasonography used to examine kidney,
Gall bladder and other organs. It is also used to check the development of an unborn baby in a mother's body.
b):- In surgery to remove cataract and break stones formed in fall bladder.
c):- Other applications include cleaning of dishes and small electronic items, making perfect homogenous solution and making holed amd cuts in glasses etc.
9:- Sonic Boom
A speed greater than the speed of sound is called supersonic speed.
A shock wave results when an aircraft travels at supersonic speed. These shock waves carry a great amount of energy. The air pressure variation associated with shock waves produces a burst or cracking sound called 'sonic boom'.
10:- Echo
Echo is the repetition of sound which is caused by the reflection of the original sound by a large and hard obstacle.
Conditions for the production of Echo
1):- Minimum gap between the original sound and the reflection of original sound
2):- For echo to be heard, the minimum distance between the source of sound and the obstacle is 17 m.
3):- Nature & Side of object
The obstacles should be hard and of large size.
11:- Echolocation
The use of reflected sound waves to find objects is called echolocation.
Animals such as dolphins, bats use echolocation to hunt food and to find objects in their paths. The property of sound is used in
𝙎𝙊𝙉𝘼𝙍 (𝙎𝙤𝙪𝙣𝙙 𝙉𝙖𝙜𝙞𝙫𝙖𝙩𝙞𝙤𝙣 𝙧𝙖𝙣𝙜𝙞𝙣𝙜) to measure the depth of the sea and to locate objects such as shoals of fish under the sea.
12:- Characteristics of sound
Three main characteristics of sound:-
1- loudness
2- Pitch
3- Quality (timber)
a:- Loudness– It is a measure of how well a sound can be heard. The loudness of a sound depends on the amplitude. The larger the amplitude, the louder the sound and the smaller the amplitude, the softer the sound.
Loudness is directly proportional to the square of the amplitude of the vibration producing the sound.
SOUND DECIBEL LABEL
whispering 20 db
Normal Conversation 60 db
Loud (cheering) 70-80 db
Loud, sterio, lightning 100-110 db
Discomfort & Pain 120 the above
1- Loudness increases with frequency of the wave and the density of the medium. It also increases with surface area of the Vibrating body.
2- Loudness decreases with the distance of the source of sound.
b:- Pitch :- This characteristics of sound differentiate a shrill sound from a flat sound. If the frequency is high then the vibration are fast, then the sound is high pitched or shrill. If the frequency is low , the vibration are slow, then the sound is low pitched or flat.
C:- Quality or Timbre
Quality or timbre is that characteristics of sound which makes it possible to distinguish one sound from the other even though they may be of the same pitch and loudness. For example, it is possible to distinguish the voice of two person on telephone by first say hellow, or the sound produced by a guitar and a sitar.
13 :- Music and Noise
Music consists of sound waves that are produced by regular and periodic vibrations while noise is produced when vibration are irregular and non-periodic.
A noise consists of random mix of frequencies resulting in irregular patterns of waves. Music is pleasant and discordant soothing to the ears while noise is hard and unpleasant.
Noise pollution:- Noise pollution is caused by fast moving vehicles, ships, trains, aeroplanes, loudspeakers, etc. Noise pollution can cause many disease like blood pressure, heart attack, hearing loss, headaches etc.
14:- How Sound is detected by our Ear
Our ear is divided into three parts
– outer ear, middle year and inner ear.
a):- The outer ear acts as a funnel for sound waves. The pinna collects sound waves and directs them into the ear canal.
b) :- In the middle ear, there are three bones – the hammer, anvil and stirrup they acts as levers to increase the size of the vibration.
c):- In the inner ear, vibrations created by sound are changed into electrical signals and sent to the brain.
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