Wave Optics

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What is Wave Motion

When a particle moves through space, it carries KE with itself, wherever the particle goes, the energy goes with it. (one way of transport energy from one place to another place). There is another way(wave motion) to transport energy from one part of space to another without any bulk motion of material together with it. Sound is transmitted in air in this manner only. Few examples of waves: The ripples on a pond, the sound we hear, visible light, radio and TV signals, etc.


Classification of Waves

Classification of Waves According To

  1. Necessity of Medium:

  1. Mechanical or elastic wave

  2. Electromagnetic wave

  1. Propagation of Energy:

               A. Progressive

               B. Stationary

  1. Dimensions:

               A. One dimensional

               B. Two dimensional

               C. Three dimensional

  1. Vibration of Particle:

               A.Transverse

               B. Longitudinal


  1. Based on Medium Necessity: A wave may or may not require a medium for its propagation. The waves which do not require a medium for propagation are known as non-mechanical waves. Example: light, heat, radio, waves, etc. on the other hand waves which require medium for propagation are called mechanical waves. Example: elasticity and density. For this reason elastic waves are known as mechanical waves.

  2. Based on Energy Propagation: Waves can be divided into two parts on the basis of energy propagation.

  1. progressive waves  

  2. Stationary waves

The progressive wave propagates with fixed velocity in a medium. In stationary wave particles of the medium vibrate with different amplitude but energy do not propagate.

  1. Based on Direction of Propagation: Waves can be one, two or three dimensional according to the number of dimensions in which they propagate energy. Waves moving along strings are one dimensional. Surface waves or ripples on water are two dimensional, while sound waves from a point source are three dimensional.

  2. Based on Motion of Particles of Medium: Waves are of two types on the basis of motion of particles of the medium.

  1. Longitudinal Waves: In this type of waves, oscillatory motion of the medium particles produces regions of compression(high pressure) and rarefaction(low pressure) which propagate in space with time.

The region of high particle density is called compressions and the region of low density is called rarefactions. The propagation of sound waves in air is visualised as the propagation of pressure or density fluctuations. The pressure fluctuations are of the order 1Pa, whereas atmospheric pressure in 100000Pa.

  1. Transverse Waves: In transverse wave the direction associated with the disturbance(i.e motion of articles of the medium) is at right angle to the direction of propagation of wave. 

Mechanical waves produced in a medium which have shearing property are known as shear waves or S-wave. Shearing is a property of the body by its shape on application of force. Mechanical transverse waves are generated only in solids and the surface of liquid. In this individual particles of the medium execute SHM( simple harmonic motion) about their mean position perpendicular to direction of propagation of wave motion. A crest is a portion of the medium, which is raised temporarily above the normal position of the rest of particles of the medium, when a transverse wave passes. Where a trough is a portion of the medium which is depressed temporarily below the normal position of a particle of the medium, when a transverse wave passes.


Fundamental Facts of Mechanical Wave Motion

Essential property of medium for propagation of mechanical wave:

1. Elasticity: By virtue of this property displaced medium particles regain their mean position.

2. Inertia of Medium: with this property medium has ability to store energy in one form to another form.

3. During energy transfer their particles execute simple harmonic motion.

4. During wave propagation all particles execute the same type SHM.

5. The direction in which energy propagates is the direction of the wave.


Fundamental Elements of Mechanical Wave Motion

  1. Amplitude of wave: it is denoted by a.

  2. Time period of wave: (T)

  3. Frequency of wave: (n)

  4. Angular frequency

  5. Wavelength of wave

  6. Propagation constant: (k)

  7. Speed of wave: V=D/t

  8. Velocity of particle


Superposition of Waves

Two or more waves can transverse the same medium without affecting the motion of one another. If several waves propagate in a medium simultaneously, then resultant displacement of any particle of the medium at any instant is equal to the vector sum of the displacement produced by individual waves. The phenomenon of intermixing two waves to produce new waves is called superposition of waves. Therefore according to superposition principle.


Due to Superposition of Waves the Following Phenomenon Is Seen:

1. Interference: Superposition of two waves of nearly equal frequency in the same direction.

2. Beats: Superposition of two waves of nearly equal frequency in same direction.

3. Stationary Waves: Superposition of equal wave from opposite direction.

4. Lissajous’ Figure: Superposition of perpendicular wave.

FAQ (Frequently Asked Questions)

1. What is Wave Optics?

When a particle moves through space, it carries KE with itself, wherever the particle goes, the energy goes with it. (one way of transport energy from one place to another place). There is another way(wave motion) to transport energy from one part of space to another without any bulk motion of material together with it.

2. Classify Waves in Very Short Form?

Classification of Waves According To

  1. Necessity of Medium:

               A. Mechanical or elastic wave

               B. Electromagnetic wave

  1. Propagation of Energy:

               A. Progressive

               B. Stationary

  1. Dimensions:

               A. One dimensional

               B. Two dimensional

               C. Three dimensional

  1. Vibration of Particle:

               A.Transverse

               B. Longitudinal

3. Explain Superposition of Wave?

Two or more waves can transverse the same medium without affecting the motion of one another. If several waves propagate in a medium simultaneously, then resultant displacement of any particle of the medium at any instant is equal to the vector sum of the displacement produced by individual waves. The phenomenon of intermixing two waves to produce new waves is called superposition of waves.