Assertion :If we use two solution lamps illuminating two pinholes , we dont observe interference fringes Reason: Light wave emitted from an ordinary source (like a sodium lamp) undergoes abrupt phase changes in times of the order in 10−10s.
A
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
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B
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
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C
Assertion is correct but Reason is incorrect
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D
Both Assertion and Reason are incorrect
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Solution
The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
The assertion is true. As we see interference fringes if the sources are spatially coherent.
And at any instant in time there will be places where the intensity is high and places where it will be low. Because the two light sources are not coherent that is to say they do not have a fixed phase relationship, the positions of these light/dark areas changes very rapidly - make a guess of every 10−10 second. What you see is a time-averaged intensity - which is the uniform illumination of the screen.