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Explain, using Huygen's principle, how diffraction is produced by a narrow slit which is illuminated by a monochromatic light. Show that central maximum is twice as wide as the other maxima and the pattern becomes narrower as the width of the slit is increased. |
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Answer» Solution :When a plane wavefront of monochromatic light is incident on a narrow slit, each point of slit behaves as a secondary source of light in accordance with Huygen.s principle. These secondary sources emit wavelets which travel in DIFFERENT directions. Naturally wavelets emitted by a different PARTS of the single narrow slit superpose. as a result to superposition we obtain a broad pattern with central brigh region and on both sides there are alternate dark and BRIGHT regions. thus, intensity distribution on screen is redistributed. this phoenomenon is called diffraction of light due to a narrow slit. It can be easily shown that positions of minimas are given on the screen by `x=pm(nDlamda)/(a)`, where n is any integer a=slit WIDTH and D=distance of screen from the slit. `therefore` Width of nth maximum is twice as WIDE as the other maxima. |
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