Waves have a very important place in human existence. They are exhibited in both; the best and the worst of creations of human beings. Without waves we won’t be able to hear the most beautiful scores of music, without them the most power bombs would have no effect. They are present in all spheres of human existence. Light and heat without which life would not have been possible, reach earth in form waves. Destructive power of a bomb strikes us in form of waves. Wave is a medium through which energy flows. Waves are present in every form of nature. Our understanding of the physical world is not complete until we understand the nature, properties and behaviors of waves. This article will help you to appreciate how beautifully god has devised the phenomenon of waves.

Let’s start with a simple example of a wave moving across the surface of an ocean, lake, pond or other body of water. The waves are created by some form of a disturbance, such as: when a rock is thrown into the water. The water wave has a crest and a trough and travels from one location to another. One crest is often followed by a second crest which is often followed by a third crest. Every crest is separated by a trough to create an alternating pattern of crests and troughs. A duck or gull at rest on the surface of the water is observed to bob up-and-down at rather regular time intervals as the wave passes by. The waves may appear to be plane waves which travel together as a front in a straight-line direction, perhaps towards a sandy shore. Or the waves may be circular waves which originate from the point where the disturbances occur; such circular waves travel across the surface of the water in all directions. These mental pictures of water waves are useful for understanding the nature of a wave and will be revisited later.

We know that energy regularly flows from one location to another location and wave is a medium through which energy flows.

A transverse wave is a wave in which the particles of the medium are displaced in a direction perpendicular to the direction of energy transport. A transverse wave can be created in a rope if the rope is stretched out horizontally and the end is vibrated back-and-forth in a vertical direction.

The dashed line drawn through the center of the diagram represents the equilibrium or rest position of the string. This is the position that the string would assume if there were no disturbance moving through it. Once a disturbance is introduced into the string, the particles of the string begin to vibrate upwards and downwards. At any given moment in time, a particle on the medium could be above or below the rest position.

CRESTS

Points A and F on the diagram represent the crests of this wave. The crest of a wave is the point on the medium which exhibits the maximum amount of positive or upwards displacement from the rest position.

TROUGH

Points D and I on the diagram represent the troughs of this wave. The trough of a wave is the point on the medium which exhibits the maximum amount of negative or downwards displacement from the rest position.

AMPLITUDE

The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position. In other words, the amplitude is the distance from rest to crest.

WAVELENGTH

The wavelength of a wave is simply the length of one complete wave cycle. The wavelength can be measured as the distance from crest to crest or from trough to trough. In fact, the wavelength of a wave can be measured as the distance from a point on a wave to the corresponding point on the next cycle of the wave. In the diagram above, the wavelength is the distance from A to E, or the distance from B to G, or the distance from E to J, or the distance from D to I, or the distance from C to H. Any one of these distance measurements would suffice in determining the wavelength of this wave.

LONGITUDINAL WAVE

A longitudinal wave is a wave in which the particles of the medium are displaced in a direction parallel to the direction of energy transport. A longitudinal wave can be created in a slinky if the slinky is stretched out horizontally and the end coil is vibrated back-and-forth in a horizontal direction. If a snap-shot of such a longitudinal wave could be taken so as to freeze the shape of the slinky in time, then it would look like the following diagram.

Because the coils of the slinky are vibrating longitudinally, there are regions where they become pressed together and other regions where they are spread apart.

A region where the coils are pressed together in a small amount of space is known as a compression. A compression is a point on a medium through which a longitudinal wave is traveling which has the maximum density.

A region where the coils are spread apart, thus maximizing the distance between coils, is known as a rarefaction. A rarefaction is a point on a medium through which a longitudinal wave is traveling which has the minimum density.

Points A, C and E on the diagram above represent compressions and points B, D, and F represent rarefactions. While a transverse wave has an alternating pattern of crests and troughs, a longitudinal wave has an alternating pattern of compressions and rarefactions.

As discussed above, the wavelength of a wave is the length of one complete cycle of a wave. For a transverse wave, the wavelength is determined by measuring from crest to crest. A longitudinal wave does not have crest; so how can its wavelength be determined? The wavelength can always be determined by measuring the distance between any two corresponding points on adjacent waves. In the case of a longitudinal wave, a wavelength measurement is made by measuring the distance from a compression to the next compression or from a rarefaction to the next rarefaction. In the diagram above, the distance from point A to point C or from point B to point D would be representative of the wavelength.

Behavior of Waves

Echo

As a wave travels through a medium, it will often reach the end of the medium and encounter an obstacle or perhaps another medium through which it could travel. A sound wave is known to reflect off high walls or mountains or other obstacles to produce an echo. A sound wave traveling through air within a canyon reflects off the canyon wall and returns to its original source.

When a crest of the sound wave reaches the end of a medium, i.e., air, when air encounters a wall of a mountain, the last particle of the medium A receives an upward movement. This particle is attached to the first particle of the other medium (medium B) on the other side of the boundary. As the last particle of medium A pulls upwards on the first particle of medium B, the first particle of medium B pulls downwards on the last particle of medium A. since particles in medium B, i.e., a wall or a mountain wave is not able to travel through it and is reflected back into air, just like mirror, that is how we hear echo.