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प्रश्न
Use Huygens’s principle to explain the formation of diffraction pattern due to a single slit illuminated by a monochromatic source of light.
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उत्तर
Consider a parallel beam of monochromatic light is incident normally in a slit of width b as shown if figure. According to Huygens’s principle every point of slit acts as a source of secondary wavelets spreading in all directions. Screen is placed at a larger distance.
Consider a particular point P on the screen receives waves from all the secondary sources. All these waves start from different point of the slit and interface at point P to give
Point P0 is at bisector plane of the slit. At P0, all waves are traveling equal optical path. So are in phase the waves thus interface constructively with each other and maximum intensity is observed. As we move from P0, the wave arrives with different phase and intensity is changed. Intensity at point P is given by
`I = I_0 (sin^2α)/alpha`
where `alpha = pi/lambda b sin theta`
For central maxima α = 0 thus,
I = I0
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