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# Waves

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 Sub Topics What makes a wave a wave? A wave can be described as a disturbance that travels through a medium from one location to another location. Consider this example the first thought concerning waves invokes up a picture of a wave moving across the surface of an ocean, lake, pond or other body of water. The characteristic of a wave as an energy transport phenomenon distinguishes waves from other types of phenomenon. Waves are seen to move through an ocean or lake; yet the water always returns to its rest position.Energy transferred from each layer to other in an ocean Waves are said to be an energy transport phenomenon. As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other. The wave is defined as the energy transferred through medium with regular vibration or oscillating motion. A few examples of waves are:  water wave, light wave, electromagnetic wave, sound wave, seismic wave (earthquakes).

## What are Waves?

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A wave can be described as a disturbance that travels through a medium, transporting energy from one location to another location without transporting matter. Each individual particle of the medium is temporarily displaced and then returns to its original equilibrium positioned. The highest point on a wave is called the peak. The lowest point is called the trough. The peak of a wave and the trough of a wave are always twice the wave's amplitude apart from each other.

## Properties of Waves

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Waves possess their own properties and nature. There are many things in waves like wavelength, velocity, amplitude, pulse and frequency. Few properties are mentioned below:

Wavelength ($\lamda$): The wavelength is the distance from one wave top, or crest, to the next. It is measured in meters (m).

Amplitude (x): The amplitude is the height of the wave. It is measured in meters (m).

Frequency (f):  It is the number of waves passed through a point in 1 second. It is expressed as f.

Velocity: Velocity of a wave is the distance moved by a wave in the given time (T). It is given as

## Types of Waves

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There are three types of waves existing in nature:
Mechanical waves are that what propagates through a material medium at a wave speed and it depends on elastic and inertial properties of that medium. They are of two types

## Wave Theory

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Huygens was first to propose the wave theory. It tells that light is transmitted in the form of waves. With this he could explain the phenomenon of reflection, refraction, interference and diffraction. There was a confusion in this that if wave cannot move without a medium. Then how can it move in vacuum? Hence Huygens gave concept of ether. He told that ether pervades every where in universe. This was disproved by Michelson and Morley experiment. So wave theory was doubtful again.

After so many theories came the De-Broglie theory that states that every moving particle is associated with a wave. The wavelength of the wave is given by

Here h is a Planck constant
m is mass of particle,
v is velocity of particle.
This theory was satisfactory in all phenomena and hence was considered.

## Wave Energy

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You may visit the beaches nearby. You could see there a layer of water transferring energy toanother layer and another layer to the next layer and so on. This is what wave energy is.
Wave energy is nothing but energy carried as waves. Energy of the waves is all due movement of wave up and down. In a diagram shown below you could take a particular point on the wave moves up and down as the wave moves in a right direction. There is a turbine wheel shown in figure.

As any point of wave moves up and down that makes the wheel to rotate in anticlockwise direction. This rotation makes the turbine to produce electricity. In this way the vertical movement gets converted into rotational movements that makes the turbine move and generate electricity.

## Wave Speed

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Wave speed is the speed at which a wave travels. Wave speed is related to wavelength, frequency, and period by the equation wave speed = frequency x wavelength. The most commonly used wave speed is the speed of visible light, an electromagnetic wave. Wave speed is that what tells with at what speed the crust or trough of a wave moves in a given time. It has the same relationship as speed, distance and time which is given as:

The wave speed varies for each type of wave. If a wave covers a distance $\lambda$ in time T. The wave speed is

## Wave Frequency

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The frequency ( ) of a wave is the number of oscillations per unit time. The frequency suggests us how often something can happen. The frequency of a wave tells us how many waves cycles passes through a point per second. The unit of frequency is expressed as per second (s-1) called as Hertz (Hz).

## Wavelength

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Wavelength is a length what a single wave cycle occupies at any instant. It can be taken between the leading edge of one cycle to the leading edge of next cycle. It is symbolized as $\lambda$.
Here $\lambda$ = wavelength,
v = velocity of wave,
f = frequency in Hz.

## Period of a Wave

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The period (T) of a wave is the time that it takes for one complete oscillation. The unit of period is the second. Wave period tells how much time it takes for one cycle to pass in a given time. Faster a wave moves smaller will be its wave period which can be got by knowing how much time it takes for two peaks to pass through a certain point.

## Standing Waves

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It is a combination of two waves moving in opposite directions, each having the same amplitude and frequency. A standing wave pattern is a vibrational pattern created within a medium when the vibrational frequency of the source causes reflected waves from one end of the medium to interfere with incident waves from the source. The phenomenon is the result of interference.
Stationary waves may be set up when a wave reflects back from a surface and the reflected wave interferes with the wave still travelling in the original direction. They have two points’ nodes and antinodes. Nodes are the stable points having no displacement. Midway to the two nodal points there is a point undergoing maximum displacement called Antinodes.

## Electromagnetic Waves

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Electromagnetic waves are waves which can travel through the vacuum of outer space. Mechanical waves, unlike electromagnetic waves, require the presence of a material medium in order to transport their energy from one location to another. Electromagnetic waves are created by the vibration of an electric charge. The actual speed of an electromagnetic wave through a material medium is dependent upon the optical density of that medium.
Electromagnetic waves are that consists of oscillating electric and magnetic waves coupled showing periodic variations at right angles to each other to the direction of propagation. These pass through vacuum along with matter.
Example: Micro waves, x-rays, light waves etc.

## Sound Waves

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This wave is discovered in 1654 by Otto Von Guericke. . Sound Waves are the mechanical waves which can cause the sensation of hearing. These waves are produced by bodies vibrating at frequencies lying between the range of 20Hz and 20,000Hz perceived by the human ear. Ordinarily, we hear sound transmitted through the air. Unlike light, Sound cannot pass through vacuum. Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving.
If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves. Sound propagates as a disturbance from a point to another using medium. These waves are known as sound waves. The sound waves are mechanical got as a result of back and forth vibration of the particles in a medium. The demonstration of sound is done using the tuning fork. The vibrating of tuning fork sets the sound box in vibrational motion and that gives out the sound waves.