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MODEL PAPER 8 — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsMODEL PAPER 81 Mark
Question
Assertion (A): Light from two coherent sources is reaching the screen. If the path difference at a point on the screen for yellow light is $\frac{3 \lambda}{2}$, then the fringe at that point will be coloured.
Reason (R): Two coherent source always have constant phase relationship.
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Answer

(d) A is false but R is true. 
Explanation: When the source is emitting yellow light, then there will be a dark fringe at a point where path difference is $\frac{3 \lambda}{2}$ [from condition for dark fringe $x=(2 n+1) \frac{\lambda}{2}$ ]. If the light is white then the fringe will be coloured, the yellow and neighbouring colours being absent.

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