Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsWave Optics3 Marks
Question
What is the nature of the interference pattern obtained using white light?
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Answer
With white light, one gets a white central fringe at the point of zero path difference along with a few coloured fringes on both the sides, the colours soon fade off to white. The central fringe is white because waves of all wavelengths constructively interfere here. For a path difference of $\frac{1}{2} \lambda_{\text {walst }}$ complete destructive interference occurs only for the violet colour, for waves of other wavelengths, there is only partial destructive interference. Consequently, we have a line devoid of violet colour and thus reddish in appearance. A point for which the path difference $=\frac{1}{2} \lambda_{\text {rad }}$ is similarly devoid of red colour, and appears violettish. Thus, following the white central fringe we have coloured fringes, from redolish to violettish. Beyond this, the fringes disappear because there are so many wavelengths in the visible region which constructively interfere that we observe practically uniform white illumination.
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