Wave and optics

When a tuning fork is struck against a rubber pad and held over a resonance tube, a feeble sound is heard. However, if the length of the air column in the tube is so adjusted that the natural frequency of the air column equals the frequency of the tuning fork, resonance occurs and the air column in the tube vibrates with maximum amplitude. Due to this, an intense sound is heard.

When tuning fork struck against a rubber pad is held close to the sonometer wire without touching the sonometer board, only a small amount of air is set into vibration. This vibration is less enough to cause vibration in the sonometer wire. However, if the stem of the vibrating fork is pressed against the board of the sonometer box through the board. Since a large amount of air has been set into vibration, the vibration is quite enough to cause vibrations in the wire. It is, therefore, the vibration of the sonometer wire is distinct only when the stem of the tuning fork is pressed against the board.

In fact, the intensity of sound produced by a vibrating body for a given external force is directly proportional to the density of the body. Since metal has a much higher density than the wood, the intensity produced by a metal bell is much than the intensity produced by a wood bell of the same dimension for than same force. As a result, louder sound can be produced by metal bells. In addition, the damping of sound waves in wood is much more than the damping in metal. Due to this, metal bells ring for a longer time than the wooden bells do. So, it is clear that the sound coming from a metal bell is louder and longer-lasting than that coming from a wooden bell. For these reasons, the bells are made up of metal but not of wood.

u00a0If, in a wave motion, the particles of the medium propagating the wave vibrate in a direction perpendicular to the direction of propagation, the wave motion is called transverse wave are light waves, heat radiations, etc.

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If, in a wave motion, the particles of the medium propagating the wave vibrate in the direction of propagation, the wave motion is called a longitudinal wave. For example, the compressional waves in the string, sound waves, water waves, etc.

The properties of longitudinal waves are as follows:

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u00b7u00a0 u00a0 The particles of the medium always vibrate in the direction of propagation

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u00b7u00a0 u00a0 At any time, different particles have different displacements.

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u00b7u00a0 u00a0 All particles have the same amplitude.

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u00b7u00a0 u00a0 The wave travels in the form of compression and rarefaction in the medium.

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u00b7u00a0 u00a0 The velocity of each particle is maximum at the mean position and zero at extreme positions.

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u00b7u00a0 u00a0 There is a gradual phase difference between successive particles.

The following points differentiate one from the other.

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Transverse Wavesu00a0

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1. Particles of the medium propagating the waves vibrate perpendicular to the direction of propagation.

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2. It cannot travel through gas and liquid since their rigidity is zero

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3. It travels in the form of crest and trough.

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4. It can be polarized.

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Longitudinal Waves

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1. Particles of the medium Propagating the waves vibrate along the direction of propagation.

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2. It can travel through solid liquid and gas since all of them have bulk.

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3. It travels in the form of compression and rarefaction.

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4. It cannot be polarized.

A wave is a disturbance from an equilibrium condition that propagates or travel with finite velocity from one region of space to another region of space. It is due to the repeated and periodic harmonic motion of the particles of the medium about their equilibrium positions called mean positions. For example, the wave that travels through the surface of the water is called water waves. Other examples of waves are mechanical waves, electromagnetic waves, radio waves, etc.

Of course, a medium is necessary for the propagation of a wave. However, it does not mean that the materials medium is necessary for all waves for their propagation. In a vacuum, Scientists believe that there exists a hypothetical medium called ether medium which is highly rigid and tenuous and the light travels through the ether medium. When light travels through the ether medium, the ether particles vibrate about their mean positions, and the disturbance is propagated from one region to another region in the space. However, the sound waves are mechanical waves that need materials medium for their propagation. Since the ether is a nonmaterial medium, the sound waves cannot travel through it.