General Waves Properties

Introduction

We experience the impacts of waves every day in our daily life. Every sound we listen to depends on sound waves.  Every sight we see depends on light waves.  A little wave can travel across the water in a glass, and a very large tide can travel over the sea. 

Sound waves, light waves, and water waves appear very different. 

So, what similarities do all these different forms of waves have? 

What, exactly, is a wave? 

What are the characteristics of a wave? 

We will study it all in detail in this unit.

Waves and the Nature of Waves

"A method that transports energy from one point to another without transferring matter is called a wave".

Formation of waves

Disturbance of medium cause of formation of wave-like, we can produce waves by using a rope, slinky spring, and water waves in ripple tanks. Let us discuss them in detail.

Wave Motion by using a Rope

We can produce waves on a rope by attaching one end to a wall and continuously moving the other end up and down, as shown in the figure:

These up-and-down movements produce oscillations or vibrations. We can observe that the generated rope waves travel towards the wall, whereas the rope itself moves only up and down. The rope is the medium through which the waves travel or propagate.

Waves in a Slinky Spring

A slinky spring is a pre-compressed helical or coiled spring as shown in fig 1.2.

We can perform several experiments with a slinky in the laboratory to understand the phenomenon of different types of wave motion.

Attach one end of the spring with a wall. Now moving the free end of the slinky horizontally left and right continuously on the table will be able to see the coils of the spring moving left and right, whereas humps travel to the other end (10.3) (a,b,c).

Now moving the free end of the attached wall slinky spring continuously back and forth as horizontally shown in fig 1.4.

 

You can observe the individual coils moving forwards and backward. Where the coils are compressed, are seen traveling from the fixed end to the other end.

In both of the above experiments, the slinky spring is said to be the medium through which the waves travel or propagate.

Water wave in (Ripple Tank)

"A ripple tank is a shallow glass tank of water used to demonstrate the basic properties of waves".

It is a particular type of wave tank. The ripple tank is usually illuminated from above so that the light shines through the water to visualize the wave being produced.

In the laboratory, we can produce water waves with the ripple tank. In the ripple tank, a small vibrator moves up and down the water surface, resulting in the water particles at the surface that are in contact with the dipper being made to move up and down. 

This up and down motion soon spread to other parts of the water surface in the tank in the form of ripples; fig. 1.5. Here the water is the medium through which the ripples travel or propagate.

Types of Wave Motion

The direction in which the displacement takes place within a wave motion affects the properties of the wave. 

These wave types can be illustrated using a slinky, long flexible steel coil or spring, which rests on a smooth table during use. 

Wave energy can be transmitted, for example, by a slinky, and for illustrations, each of the coil turns can represent a particle of the medium through which a wave is traveling.

Transverse Wave

The slinky illustrates the transverse wave in Fig. 1.6. Move the free end of the slinky up and down repeatedly. 

These up and down movements of the coils produce oscillations. 

Have you noticed that when coils move up and down, the direction of the wave motion is perpendicular to the direction of oscillation?  We call this type of wave a transverse wave; Fig. 1.7.

In the light of the above experiment, transverse waves can be defined as:

Definition: "Transverse waves are waves that travel in a direction perpendicular to the direction of wave motion".

Transverse wave motion can also be observed on the surface of the water in a pond or a ripple tank, as vibrations in a guitar string. Another essential type of transverse wave is electromagnetic waves, e.g., light waves. microwaves, radio waves.

Amplitude

Definition: "Amplitude is the maximum displacement moved by a point on a vibrating body from the rest or mean position".

It is the height of a crest or depth of a trough measured from the rest position as shown in fig 1.8. Its SI unit is meter (m).

Crest

Definition: "A crest is a point on a surface wave where the displacement of the medium is at a maximum." 

OR 

"The positive/upper part of the wave is called the crest".

Trough

Definition: "The trough is a point on a surface wave where the displacement of the medium is at a minimum".

Longitudinal Wave

The slinky illustrates the longitudinal wave in Fig. 1.9. Move the free end of the slinky forward and backward (i.e. push and pull) to expand and compress the slinky repeatedly. 

These forwards and backward movements of the coils produce oscillations. Have you noticed that when coils move forwards and backward, the direction of the wave motion is parallel to the direction of oscillation? We call this type of wave a longitudinal wave Longitudinal waves can be defined as:

Definition: "Longitudinal waves are waves that travel in a direction parallel to the direction of wave motion"

Another common example of a longitudinal wave is sound waves.

Compression

Definition: "Compression in the longitudinal waves is a region where turns of the coil or particles are closer together than average".

Rarefaction

Definition: "Rarefaction, in the longitudinal waves, is a region where turns of the coil or particles are further apart than average".

Read more...

What is a wave?

Types of waves