Sound class 9 notes

Sound 

Sound wave:-A sound is a form of energy that is produced by a vibrating object. These vibrations Continue to and give the sensation of hearing.

Production of the sound and propagation of sound

Sound is produced when we vibrate any object and vibrating objects disturb the particles of the medium through which sound travel. These vibrations are continued to move the particle and reach at another end.

Diagram

How the vibrations transferred by A tuning fork

The vibrations are transferred by the tuning fork by consecutive compression and rarefaction regions.

Compression

It is the reason in a medium where the leg of tuning fork moves outward and creates the region of high pressure which is called the compression region.

Rarefaction region

it is a region in a medium where there is high density,is called rarefaction region.

Mechanical waves:- The waves which required the medium to travel from one place to other place, that waves are known as Mechanical waves. For example, Sound wave.

Non-Mechanical waves:- The waves which do not require the medium to travel from one place to another place, that waves are known as Mechanical waves. For example, Lightwave.

Amplitude:- It is defined as the maximum distance on either side of the mean position is called The amplitude of the wave.

Unit: It has a unit meter.

Wavelength:- The wavelength of a wave is defined as a change in density from maximum to minimum and again to a maximum is called one vibration or oscillation is completed, and a distance between two consecutive maximum or minimums is called its wavelength.

Unit It has unit meter.

It is represented by the symbol lambda (λ).

Diagram

Frequency:- The frequency of a wave is defined as no. of oscillations completed in one second is called the frequency of a wave.

Or

It is defined as the reciprocal of the time period.

Unit It has a unit per sec or Hertz (Hz).

Time Period:- It is defined as the Time taken by a wave to complete its one oscillation or vibration.

Unit:- It has a unit Second (s)

It has a symbol, T.

The relation between Frequency and time period:-

If Frequency is represented by f and Time period is represented by T.

Then according to the definition of frequency (It is defined as the reciprocal of the time period.)

OR

For example, if a wave completes 10 vibrations in one second. Then, the frequency of the wave is  10 Hz and the time period of the wave is 0.1 sec.

Crest:- the elevation in a wave is Crest.

Trough:- The deviation in a wave is called trough.

Characteristics of a Sound Wave:-

There are mainly three characteristics of sound.

• Loudness
• Pitch
• Quality

Loudness:- Loudness is the characteristics of a wave that differentiates two waves, out of which is louder wave and which is a softer wave. 

Factors on which loudness depends:- 

Loudness  depends on  Amplitude

Loudness  depends on   Surface area of the vibrating body

Loudness    depends on inverse of the square of the distance between sound source and listener

that means

1. The Loudness of a sound is directly proportional to the amplitude of the sound wave. More is the amplitude of a sound wave more will the loudness of that sound wave.

2. Loudness is directly proportional to the surface area of the vibrating object. More is the surface area of the vibrating objects more is the loudness of the sound wave.

3. The loudness of the sound is inversely proportional to the square of the distance between sound source and listener. It means higher will be the distance between the source and listener than lower will be the loudness.

Pitch :-

It is the characteristics of a sound that differentiate two sounds out of which one is shrill and the other one is gravel.

the pitch of a sound depends on the frequency of the sound wave.

More is the frequency, higher is the pitch.

The intensity of the Sound wave:-

It is defined as the energy of the wave passes per unit area per unit time.

Unit:- It has a unit watt per sq.metres.

Formula

Difference Between Loudness and intensity

Loudness 1. It is the measure of sensation produced in the ear. 2.It varies from person to person. 3. It has units decibel (dB) 4. loudness depends on the listeners' ears. 5. It cannot be measured.

Intensity 1. It is the energy per unit area per unit time. 2.it does not vary from person to person. 3. It has unit W/m2 4. It depends upon the source of the sound. 5. It can be measured.

Quality:-  It is that characteristic of a sound which differentiates two sound who are having the same loudness and pitch.

Tone:-  A sound of a single frequency is called tone or Pure Note. For example, tuning fork produces a vibrations of single frequency.

Note:-  A sound which is a mixture of several frequencies is called Note.

Difference between Mechanical and Non-Mechanical

Mechanical wave	Non-mechanical wave.
1.      The wave that needs a medium to move from one point to others is called a mechanical wave. 2.      For e.g. sound wave. 3.      It travels with less speed.	1.      The wave that does not need a medium to move from one point to another is called a non-mechanical wave. 2.      For e.g. light-wave 3.      It travels with a large speed.

Difference between Music and Noise:-

Music	Noise
1.      The sound which is pleasant to the ear is called Music. 2.      There is no sudden change in the amplitude. 3.      The vibration follows one another regularly. 4.      It will remove our stress, anxiety.	1.      The sound which is not pleasant to the ear is called Noise. 2.      There is a sudden change in the amplitude. 3.      The vibration does not follow one another regularly. 4.      It will cause our stress, anxiety, sleeping disturbance.

Echo:- It is defined as when a source produces a sound. It strikes with obstacle  In its way and comes back which is called reflection of the sound. It produces an echo.

Formula for echo

The velocity of the echo sound  

Or

2D = V * T

The minimum distance required to produce d an echo is 17.2 m.

Conditions for the reverberation:-

There are two conditions to encounter the reverberation of sound - 

(I) The time gap between the Sound must return to the individual after 0.1 seconds. 

(ii) For the above condition, the reflecting surface must have a distance of separation of 17.2m. It likewise relies upon temperature. 

Q:- Is the distance required to produce an echo is the same in all the seasons?

     No, the distance required to produce an echo sound is not same in all seasons because the speed of sound will increase with an increase in the temperature.

It will Changes as per the following formula:-

Reverberation:- It is defined as the propagation of the sound due to repeated reflection when the source of the sound stop omitting sound is called Reverberation.

The reverberation is necessary up to some extent and it can be reduced by the following ways:-

1. By doing sound-absorbing paint in the room.
2. By covering all the windows and doors with curtains in the room.
3. By placing proper furniture in the room.
4.  Covering roofs and walls of auditorium with sound-absorbing materials
5. The seat material is also selected on the basis of its sound-absorbing property.

The Reflection of the sound:-

Like light sound can also be reflected from the obstacle. So, it also follows the law of reflection of the sound as the light.

Law of reflection of sound:-

• The angle of incidence of the light is equal to the angle of reflection.
• The incident sound wave, reflected sound wave, and normal to the surface all lie in the same plane.

Types of waves:-

There are mainly three types of sound waves:-

• Infrasonics 
• Audible sound
• Ultrasonics

• Infrasonics:- This is a type of wave which has a frequency range from 0 Hz to 20Hz. 
• A vibrating straightforward pendulum produces infrasonic sounds.
•  Elephants and whales produce infrasonic waves.
• Seismic tremors produces infrasonic waves 
• Audible waves:- This is a type of wave which has a frequency range from 20 Hz to 20000Hz.
• Ultrasonics:- This is a type of wave which has a frequency range from 20 kHz to above. 
• Bats and whale can create ultrasonic sounds. 
• Dolphins use ultrasound to discover fish. 

Uses of the ultrasound/application of the ultrasound

1. Bats use ultrasound waves to discover their prey. 

Bats produce piercing ultrasonic squeaks. These squeaks are reflected by items, for example, prey's and are come back to the bat's ear. This permits a bat to know the separation of its prey. 

2. Dolphins use ultrasound to discover fish.

3. They are used to check babies during pregnancy. 

4. They are used for breaking stones in the kidneys into fine pieces. 

5. Echocardiography: These waves are used to take the images' hearts. This technique is called echocardiography. 

6. Ultrasonography: The method of acquiring pictures of inner organs of the body by using echoes of ultrasound waves is called ultrasonography. 

Sonar 

Sonar represents Sound Navigation And Ranging. 

Working of SONAR 

SONAR consists of a transmitter and a receptor or detector and is attached at the base of a boat. 

The transmitter produces and transmits ultrasonic waves. These waves travel through

water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are recorded by the detector. The distance of the object that reflected the sound wave

can be calculated by knowing the speed of sound in water and the time interval between

the transmission and reception of the ultrasound.

Let the time gap among transmission and reflected of ultrasound signal is t. 

Speed of sound through ocean water is v 

Total distance traveled by ultrasonic waves  = 2d. 

At that point, 2d = v × t. 

The above method is called echo-ranging.

Uses:-

The sonar technique is used to:- 

•  determine the depth of the sea.
•  to locate underwater hills, valleys, submarine, icebergs, sunken ships, etc.
•  It is also used to find the depth of the seawater.

Human Ear 

Structure of Human Ear 

The human ear can be divided into three main primary parts: Outer ear, middle ear and inner ear. 

Structure of Human Ear 

The vibrations of any sound-producing body are transmitted to our ears by the vibrating molecules of air. These vibrations first reach the outer ear.

Outer Ear:-  The outer ear consists of the pinna (which we can see from outside), ear canal, and eardrum.   

Middle ear:-  It consists of three interlocked bones hammer, anvil, and stirrup.

Inner Ear:- The inner ear consists of a coiled tube called the cochlea and auditory nerve.

Working of Human Ear 

When vibration reaches the ear, the molecules inside the canal start vibrating and strike a stretched membrane, called the eardrum.

        In the middle, these vibrations of eardrum make three interlocked bones to vibrate.

        In the inner ear, small hairs pick up vibration from the middle ear. They then send a signal to the brain via the auditory nerve, the brain converts it to make us hear a sound.