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Topic includes
- Wavefront and it's types
- Interference of light waves
- Young's experiment
- Diffraction and it's types
- Polarization and it's types
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Wave front
A source of light send the disturbance in all directions and continuous locus of all the particles vibrating in all phase in any instant is known as wavefront.
Types of wave front 🌊.
- Spherical wavefront
- Plane wavefront
Interference
Light having single wavelength is monochromatic light.
The phenomenon of redistribution of light energy in the medium due to super position of two different light waves is known as interference of light.
- At some points on screen where the intensity of light become maximum is called constructive interference.
- At some points where the light become minimum is called destructive interference.
- The alternative dark and bright bands are called fringes .
• In interference of light, the energy is neither created nor destroyed.
Intensity is directly proportional to the square of amplitude.
Young's experiment
Fringe width
The separation between two successive bright or dark fringes .
Diffraction
The phenomenon of bending of light around the corners of small obstacles or apparatus and it's consequents spreading into small regions of geometrical shadows is known as diffraction of light
Types of diffraction
- Fresnels type
The source and the screen are placed closed to aparture light after defection converges towards the screen.
Hence no lens is required to observe the fringes .
- Fraunhoffers type
The source and screen are placed at large distance. Hence , convex lens are used to observe the fringes pattern .
Polarization
It is shown by the transverse waves only not by longitudinal waves.
The phenomenon of restriction of light wave in a particular direction in a plane perpendicular to the direction of propagation of light is called polarization of light.
Unpolarized light
A light which has vibrations in all directions in a plane perpendicular to the direction of propagation is known be unpolarized light.
Examples are Sunlight, ordinary light.
Polarisers
A device that plane polarises the unpolarized light passed through it .
For example Nicol prism .
Methods of polarization
- By refection
- By scattering
- By double refraction
- By selective absorption
Polarization by reflection ( Brewster's law)
Brewster's law, relationship for light waves stating that the maximum polarization (vibration in one plane only) of a ray of light may be achieved by letting the ray fall on a surface of a transparent medium in such a way that the refracted ray makes an angle of 90° with the reflected ray.
Brewster law formula
Brewster's Law
The polarizing angle ip hinges on on the refractive index mu of the transparent material. The relation is articulated by “µ = tan ip” When unpolarized light is found to be incident on a transparent medium at any polarizing angle then the transmitted and reflected rays are vertical to each other.
Brewster angle
Brewster's angle, or the polarizing angle, is defined as an angle at which an incident beam of unpolarized light is reflected after complete polarization. The incident light with an electric field parallel to the plane of incidence usually has a zero reflection coefficient at a particular angle between 0 and 90°.
Polarization by scattering
When unpolarized light incident on second molecule the electrons in the molecule begin to vibrate in both planes parallel and perpendicular to plane of paper. The electrons vibrating parallel to the plane of paper cannot send energy towards observer looking at right angle to the direction of sunlight because their according has no transverse component. So, the light get plane polarised perpendicular to the plane of paper.
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