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Notes, Exercises, Videos, Tests and Things to Remember on Sound

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## Note on Sound

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The sound is the form of energy, which is produced by vibration of molecules of a body. Sound travels in the form of a wave. Like light, it also undergoes reflection, refraction etc.

### Wave

The path of energy, through which the energy travels is called a wave. The wave can also be defined as the periodic disturbance of the particles of the medium. The waves can be classified into two types’ mechanical waves and electromagnetic wave. Mechanical waves can be propagated only in material medium whereas electromagnetic waves do not require any material medium for propagation.

##### Wave in water surface

when a stone is dropped into a pool of water, circular waves spread out on all directions on the surface from the center of disturbance. There are circular regions called crest, where the water level is above the normal level and there are other circular regions, called trough, where the water level is below the normal level. Water waves on the surface of water are the examples of wave motion.

##### Waves in rope:

If a rope held horizontally, is fixed at one end and the free end is moved up and down at right angle, a disturbance consisting of a series of crests and troughs travel along the rope.

#### Sound wave:

A wave of compression and rarefaction, by which sound is propagated in an elastic medium such as air is known as sound wave.

Disturbance set up in a medium is called a wave and the propagation of disturbance, without involving transfer of any material within it, is called wave motion.

##### Types of wave motion

Waves can be classified into two types on the basis of the nature of the vibration in particles of the medium. They are transverse wave and longitudinal wave.

Comparison of transverse and longitudinal wave

 Transverse waves Longitudinal waves Vibrations of particles of a medium are perpendicular to the direction of propagation of wave. Vibrations of particles of a medium are along the direction of propagation of wave. These waves can be generated in solids and liquids. These waves can be generated in solids, liquids and gases. A complete wave consists of a crest and trough A complete wave consists of a compression and rarefaction. It can travel in vacuum. It cannot travel in vacuum. Speed of this wave is more. Speed of this wave is less.

image source:http://lh3.ggpht.com/-tX6BKR8nUBI/Uf8fnKlf8OI/AAAAAAAAHSE/L8k31m6xw5o/Difference between Longitudinal wave and Transverse wave_thumb[13].jpg?imgmax=800

• Sound is the form of energy, which is produced by vibration of molecules of a body. Sound travels in the form of a wave.
• The path of energy, through which the energy travels is called wave.
• Mechanical waves can be propagated only in material medium whereas electromagnetic waves do not require any material medium for propagation.
• Disturbance set up in a medium is called a wave and the propagation of disturbance, without involving transfer of any material within it, is called wave motion.
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### Very Short Questions

The sound wave carries energy from a vibrating object as kinetic energy of the particles of material medium (solid, liquid or gas), so sound waves are called mechanical waves.

The differences between transverse and longitudinal wave are as follows:
 Transverse wave Longitudinal wave It is the wave in which the particles of the medium vibrate perpendicular to the direction of the propagation of the wave. Eg: wave produced in rope and ponds. It is the wave in which the particle of the medium vibrates along the direction of the propagation of light. Eg: sound waves. These waves can be generated in solids and liquids. These waves can be generated in solid, liquid and gas.

Sound cannot travel in vacuum because sound is a mechanical wave that needs material medium to transfer energy.

The propagation of disturbance, without involving transfer of any material within it, is called wave motion. There are two types of wave motion. They are transverse and longitudional wave.

When the displacement of a particle is maximum above its mean position is called Crest. When the displacement of a particle is maximum below its mean position is called Trough

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• ### Which is not part of the electromagnetic waves?

Sound waves

Visible light

Micro waves

• ### Which electromagnetic wave is used when we change TV channels using remote?

Microwave
Ultraviolet waves
Infrared
Gamma rays

Microwave
Infrared
X-rays
Gamma rays
• ### Which electromagnetic wave is used when we receive TV channels from satellite?

Infrared

Gamma rays

Ultraviolet waves

• ### What is use of Ultraviolet rays?

To make objects visible.
To produce vitamin D.
To kill cancer cells.
To take photograph of skeleton.
• ### What is use of Gamma rays?

To make objects visible.
To take photograph of skeleton.
To kill cancer cells.
To produce vitamin D.
• ### Which is false about electromagnetic waves?

They exhibit properties of reflection and refraction.
They are unaffected by electric and magnetic waves.
Their speed in vacuum and air is same.
They are longitudinal waves.
• ### Which is true about electromagnetic waves?

They can bend around solid objects.
They are all harmful to us.
They carry energy by vibration of electric and magnetic fields.
• ### Why can't we hear sound of explosion in space?

Because there is no particle medium in space
Because explosion in space are of low power to make big enough sound
Because space is too big, sound disperses everywhere and thus we hear nothing
Because light waves interfere with sound waves
• ### The difference in compression and rarefaction region in sound wave is in

Intensity and pitch
Volume and energy
Density and pressure
Density and power
• ### What are Crest and trough?

Crest is the highest part and trough is the lowest part of transverse wave.
Crest is the highest part and trough is the lowest part of longitudinal wave.
Crest is the highest part and trough is the lowest part of transverse or longitudinal wave.
Crest is the lowest part and trough is the highest part of transverse wave.
• ### Which is not a use of ultra sound?

To break kidney stone.
To locate tumor.
To generate pictures of embryo.
To create an echo.
• ### Which is not an effect of sound?

It can cause pain in ear.
It can raise our blood pressure.
It can make us concentrate more on work.
It can make us irritable.
• ### Which is not way to reduce sound from machinery?

Using silencer in machines.

Insulating machine from environment.

Operate machine by highly trained manpower.

Using protective device by workers near the machine.

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