Waves: Introduction

What happens when you throw a stone in still water? You find circles propagating outwards, and it feels as if the water is moving. The reason is the water surface getting disturbed. But when a cork is placed on that disturbed water surface, it moves up and down rather than moving outwards with the circles. Here the water remains stagnant, and some elastic force or pattern is causing the disturbances. Clearly, the motion of one is influenced by the other. This influencing force or pattern propagating without the actual flow of matter is known as waves. There are different kinds of waves which we will discuss further in this waves introduction topic. 

Definition & Importance of waves 

A wave is a pattern of disturbances propagating through a medium, usually in space and time. It carries and transports energy while propagating from one point to another without any net movement of particles. Waves exchange energy in all our communications as it involves the transmission of signals.

Different kinds of waves platform

All communications involve different types of waves possessing different sets of characteristics. Based on the direction of energy and orientation of particle motion, waves are of three types : 

• Mechanical waves: Here, the transmission medium limits the direction of the wave propagation. Example- Sound waves, Water waves.
• Electromagnetic waves: These waves are a merger of electric and magnetic fields. Example- Light waves.
• Matter waves: These waves are related to the constituents of matter- protons, electrons, and neutrons. They are more conceptual than mechanical or electromagnetic waves. Example- They find application in electron microscopes.

Medium of propagation of waves

• Mechanical waves need a medium to propagate themselves, and they cannot propagate through a vacuum. These waves are further classified into two categories:

1. Transverse waves: These waves propagate in a direction perpendicular to displacement or disturbances. Example- ripples on the surface of water.
2. Longitudinal waves: These waves propagate in a direction parallel to the direct displacement or disturbances. Example- Sound waves.

• Electromagnetic waves don’t need any medium to propagate and can travel through a vacuum. Examples- Radio waves, Microwaves.
• Matter waves are a complicated concept related to the matter, and you will learn more about this in later studies.

Significance of Mechanical waves

The disturbances in mechanical waves propagate from one point to the other, but the orientation of the particles produces lesser oscillations about their mean position. The practical example of this applies to a stationary train connected to numerous bogies with a spring coupling. An engine is attached at one end of a train. When a push is exercised to the adjacent bogie, the same push is transported to the next one. This way, all the remaining bogies feel the same push without displacing the entire train. This way, waves exchange position without the actual transfer of the matter, in this case, the whole train.

Significance of Transverse and Longitudinal waves

• Transverse waves: We have known that when the direction of propagation is perpendicular to the oscillation of constituents of the medium, it is known as transverse waves. While propagating, these waves form alternate crests and troughs. 

Now, the question arises that how are these waves caused? The illustration of this example will fetch the answer. At the point when we pull a string in a vertical direction, the development and propagation of the waves are conceivable in light of the fact that the whole string is under tension. The little disturbance which is given at one side is the tension itself and it gets propagated to its adjoining particles and keeps on continuing. So this pulse will get transferred along the length of the string. The oscillation of the particles is at right angles to the propagation of the wave and the elements of the string oscillate about their mean position. Thus, the resulting disturbances on the string is a sinusoidal wave.

• Longitudinal waves: Here, the propagation of waves is along the direction of disturbance. So, there will be regions where particles are far apart called rarefaction and regions where particles are closer are called compression.

An illustration of longitudinal waves is given through the next example. When a long pipe is loaded up with air, it has a piston towards one side. A solitary abrupt to and fro movement of the piston will produce a rarefaction and compression in the air. There will be lower density in rarefaction and a higher density in compression. If the to and fro movement is persistent and occasional, a sinusoidal wave will be created propagating in the air along the length of the pipe. 

Key differences of Transverse and Longitudinal waves

• In transverse waves, each element is subjected to shearing stress whereas, in longitudinal waves, each element is subjected to a compressive strain.
• Transverse waves can propagate in solids and not in fluids whereas longitudinal waves can propagate through solids as well as fluids.

Conclusion

Concluding the introduction of the wave, here are some key points that you should always remember.

• In a wave platform, it is the energy that is transferred from one point to the other and not the matter. And this energy transmission takes place due to the association of the neighbouring particles of the medium by elastic forces.
• Mechanical waves are associated with the elastic properties of the medium.
• Longitudinal waves can propagate in a medium with a bulk modulus of elasticity such as solids, liquids, and gases.
• Transverse waves need mediums with a shear modulus of elasticity to propagate such as solids.
• Air can propagate on longitudinal sound (pressure) waves.