Wave Optics

A wave front is defined as the continuous locus of all particles of a medium, vibrating in same phase. Depending on the shape of source of light, wave front is of three types: Spherical wave front, Cylindrical wave front and Plane wave front. Huygens gave a hypothesis for a geometrical construction of the position of a common wave front at any instant, during the propagation of waves in a medium. Huygens principle explains the propagation of a wave front in a medium. Huygens using wave front concept successfully explained the laws of reflection and refraction of light. Doppler effect is the apparent change in frequency due to the relative motion between the source and the observer. The sources of light which emit continuous light waves of the same wavelength, same frequency and same phase or constant phase difference are called Coherent sources whereas source of light which do not emit light waves with same wavelength and a constant phase difference are called Incoherent sources. When two or more wave motions traveling through a medium superimpose on each other, a new wave is formed in which resultant displacement at any instant is equal to the vector sum of the displacements due to individual waves at that instant. Interference of light is the phenomenon of redistribution of light energy in a medium on account of superposition of light waves from two coherent sources. Thomas Young revived the wave theory of light and recognized that interference phenomena provide proof of the wave properties of light. Thomas Young’s experiment is popularly known as Young’s double slit experiment. Diffraction is the phenomenon of bending of light around corners of an obstacle or aperture in the path of light. Diffraction due to a single slit is observed when double slit in Young’s experiment is replaced by a single narrow slit. Polarisation is the phenomena of restricting the vibrations of light in a particular direction, perpendicular to the direction of wave motion. Polarised light can be produced by scattering of light through 90o in earth’s atmosphere and by reflection at a specific angle.

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