CBSE Class 12-science Answered
Diffraction from Single Slit:
When a wave front of monochromatic light propagating normally to the slit is incident on it then the diffracted light moving along the shadow region is focused by means of lens on the screen. Every point of the wave front in the plane of the slit is source of secondary wave front traveling normally to the slit. Depending upon the path difference between the secondary wave fronts from the original wave front, the condition of maximum intensity (bright) and minimum intensity (dark) patterns are observed.
Condition of Single Slit Diffraction:
The two rays are parallel at an angle from the centre axis. The path difference between these rays is equal to the (a/2) sin θ Here 'a' is the width of the slit and theta is the angle made by the wave fronts with the central axis This path difference is equal to half the wavelength of the incident which is the condition for the dark fringe = λ / 2 The general equation for condition of minimum intensity or dark fringe higher order fringes is given as (a/2) sin θ = m ( λ / 2 ) sin θ = m ( λ / a ) Where m = 1,2,3,...... This is the equation for the dark fringe in diffraction pattern.
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