### WAVES

 WAVE

A wave is a form of disturbance which travels through a material medium due to the repeated periodic motion of the particles of the medium about their mean position.A sudden and short duration disturbance is called a pulse.Waves are broadly of two types.
i. Mechanical wave
ii.Electromagnetic wave

### MECHANICAL WAVE

The wave which require material medium (solid,liquid,gas) for their propagation are called mechanical waves elastic wave Mechanical wave are of two types.
i. Transverse waves
ii.Longitudinal waves

### TRANSVERSE WAVES

In these waves,displacement of the particles of the medium is at right angles to the direction of propagation of the waves.These waves can be polarized and can travel in solids and liquids only.
These waves travel in the form of crests and troughs.

### LONGITUDINAL WAVES

In these waves, displacement of the particles of the medium is in the direction of propagation of the waves.
These waves cannot be polarized and can travel in solids,liquids and gases.
These waves travel in the form of compression’s and rarefaction’s.

### ELECTROMAGNETIC WAVES

 ELECTROMAGNETIC WAVE

The waves which do not require medium for their propagation i.e., which can propagate even through the vacuum are called electromagnetic waves.
Cathode rays, canal rays, ɑ rays,𝛃 rays sound waves and ultrasonic waves are not electromagnetic waves.
Some Important Electromagnetic Waves
 ELECTROMAGNETIC WAVES DISCOVERER WAVELENGTH RANGE FREQUENCY RANGE 𝜸-rays Henry Becqueral 10-14 to 10-10 1020 to 1018 X-rays W.Rontgen 10-10 to 10-8 1018 to 1016 Ultraviolet rays Ritter 10-8 to 10-7 1016 to 1014 Visible radiation Newton 3.9*10-7 to 7.8*10-7 1014 to 1012 Infra-red rays Hershel 7.8*10-7 to 7.8*10-3 1012 to 1010 Short radio waves or Hertz hertzian waves Heinrich 10-3 to 1 1010 to 108 Long radio waves Marcony 1 to 104 108 to 106

### SOUND WAVE

Sound is a form of energy  which produces the sensating of hearing.
Sound waves are longitudinal mechanical waves.
Sound waves have low frequency and high wavelength.
Sound waves cannot travel in vacuum.
The rebouncing back of sound when it strikes a hard surface is called reflection of sound.
The repetition of sound due to reflection of sound wave is called an echo.
According to their frequency range, longitudinal mechanical waves are divided into the following categories
1.  Audible or sound waves The longitudinal mechanical waves which lie in the frequency range 20 Hz to 20000 Hz are called audible or sound waves.These waves are sensitive to human ear.
2. Infrasonic waves The longitudinal mechanical waves having frequencies less than 20 Hz are called Infrasonic.These waves are produced by sources of bigger size such as earthquakes,volcanic eruptions,ocean waves and by elephants and whales.
3. Ultrasonic waves The  longitudinal mechanical waves having frequencies greater than 20000 Hz are called ultrasonic waves. Human ear cannot detect these waves.But certain creatures like dog,cat,bat,mosquito can detect these waves.Bat not only detect but also produce ultrasonic.

### APPLICATIONS OF ULTRASONIC WAVES

For sending signals.
For measuring the depth of sea.
For cleaning cloths, aeroplanes and machinery parts of clocks.
For removing lamp-shoot from the chimney of factories.
In sterilizing of a liquid.
In ultrasonography.
In SONAR.

### SPEED OF SOUND

The speed of sound basically depends upon elasticity and density of medium.
Speed of sound in air is 332 m/s, in water is 1483 m/s and in iron is 5130 m/s.
The speed of sound is independent of pressure i.e., speed remains unchanged by the increase or decrease of pressure.
The speed of sound in air increases by 0.61 m/s when the temperature is increases by 10C.
The speed of sound is more in humid air than in dry air because the density of humid air is less than the density of dry air.
When sound enters from one medium to another medium,its speed and wavelength changes but frequency remains unchanged.

### CHARACTERISTIC OF SOUND WAVE

Intensity : Intensity of sound at any point in space is defined as amount of energy passing normally per unit area held around that point per unit time.
Loudness depends an intensity of sound .
Unit of loudness is bel.
Pitch: The pitch of a sound is the characteristics which distinguishes between a shill and a grave.Pitch depends upon frequency.
Quality: Quality is that characteristic of sound which enables us to distinguishes between sound produced by two sources having the same intensity and pitch.

### SHOCK WAVES

A body moving with supersonic speed in air leaves behind it a conical region of disturbance which spreads continuously. Such a disturbance is called shock wave.These wave carries huge energy and may make cracks in window panes or even damage a building.

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