From Engineering Physics: Fundamentals and Modern Applications


The phenomenon of the interference of light has proved the validity of the wave theory of light. According to it, when two light waves of the same frequency and having a constant phase difference traverse simultaneously in the same region of a medium and cross each other, then there is a modification in the intensity of light in the region of the superposition, which is in general different from the sum of intensities due to individual waves at that point. This modification in the intensity of light resulting from the superposition of two (or more) waves of light is called interference. At certain points the waves superimpose in such a way that the resultant intensity is greater than the sum of the intensities due to individual waves. The interference produced at these points is called constructive interference or reinforcement, while at certain other points the resultant intensity is less than the sum of the intensities due to individual waves. The interference produced at these points is called destructive interference. Beyond the region of superposition the waves come through completely uninfluenced by each other.

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Optical Apertures
Optical apertures and optical slits control the diameter of beams from light sources.

Topics of Interest

4.4 YOUNG'S EXPERIMENT In 1801, Thomas Young performed an experiment that lead to the establishment of the wave theory of light. His arrangement consists of two small, closely spaced holes or slits,...

4.6 ANALYTICAL TREATMENT OF INTERFERENCE We shall derive an expression for the resultant intensity at any point P of the screen due to the superposition of two waves of light. Let S be a narrow slit...

4.5 EXPLANATION OF WAVE THEORY The formation of interference fringes on the screen can be explained on the basis of wave theory. When light passes through S, spherical waves spread out from S.

4.8 CONDITION FOR SUSTAINED INTERFERENCE OF LIGHT To obtain well defined interference patterns, the intensity at points corresponding to destructive interference must be zero, while intensity at the...

5.1 OVERVIEW Except for our treatment of polarization (which is a fundamental vectorial property of electromagnetic waves), we have regarded the propagation of light in geometrical terms. Hence we...