If you drop a pebble in a pond of still water, the water surface gets disturbed. The disturbance does not remain confined to one place but propagates outward along a circle. If you continue dropping pebbles in the pond, you see circles rapidly moving outward from the point where the water surface is disturbed. It gives a feeling as if the water is moving outward from the point of disturbance. If you put some cork pieces on the disturbed surface, it is seen that the cork pieces move up and down but do not move away from the center of the disturbance. This shows that the water mass does not flow outward with the circles, but rather a moving disturbance is created. Similarly, when we speak, the sound moves outward from us, without any flow of air from one part of the medium to another. The disturbances produced in the air are much less obvious and only our ears or a microphone can detect them. These patterns, which move without the actual physical transfer or flow of matter as a whole, are called waves.
Waves transport energy and the pattern of disturbance has information that propagates from one point to another. All our communications essentially depend on the transmission of signals through waves. Speech means the production of sound waves in air and hearing amounts to their detection. Often, communication involves different kinds of waves. For example, sound waves may be first converted into an electric current signal which in turn may generate an electromagnetic wave that may be transmitted by an optical cable or via a satellite. Detection of the original signal will usually involve these steps in reverse order.
Not all waves require a medium for their propagation. For example, light waves can travel through a vacuum. The light emitted by stars, which are hundreds of light years away, reaches us through interstellar space which is practically a vacuum.
A few examples of waves are – ocean waves, sound waves, light waves, earthquakes, TV and radio waves, X-rays, fiber optics, lasers, microwaves in ovens, etc.
1. Mechanical Waves:
The most familiar type of waves such as waves on a string, water waves, sound waves, seismic waves, etc. is the so-called mechanical waves. These waves require a medium for propagation, they cannot propagate through a vacuum. They involve oscillations of constituent particles and depend on the elastic properties of the medium.
Mechanical waves come in two different forms – transverse wave and longitudinal wave.
A transverse wave is a wave that causes particles over which they pass to vibrate at right angles to the direction in which the waves are moving. It moves the medium perpendicular to the wave motion. For example, picture a boat bobbing up and down in the water as a wave passes by; a vibrating guitar string, etc.
A longitudinal wave is a wave that causes particles over which they pass to vibrate parallel to the direction in which the waves are moving. It moves the medium parallel to the wave motion. For example, slinky waves that you push and pull, etc.
2. Electromagnetic Waves:
The electromagnetic waves are a different type of wave. Electromagnetic waves do not necessarily require a medium – they can travel through a vacuum. Light, radio waves, X-rays are all electromagnetic waves. In a vacuum, all electromagnetic waves have the same speed.
3. Matter Waves:
The third kind of wave is so-called Matter waves. The matter is made up of atoms, and atoms are made of protons, neutrons, and electrons. The wave function for a material particle is often called a matter wave. All matter can exhibit wave-like behavior. For example, a beam of electrons can be diffracted just like a beam of light or a water wave. They are conceptually more abstract than mechanical or electromagnetic waves; they have already found applications in several devices basic to modern technology; matter waves associated with electrons are employed in electron microscopes.
