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My professor asked me (in my viva exam), "If, in the Fraunhofer single slit diffraction experiment, if we have 2 slits instead of one (at very short distances), What would happen?"

I answered with "Young's double slit experiment intensity distribution". He said my answer was wrong. Out of curiosity, what is the right answer then?

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The intensity distribution will remain same as fraunhofer one only , however intensity will increase at each point . Means supposedly earlier there was Amplitude 2A , at a point of maxima , now it will become 4A , since 2 waves will come from the new fraunhofer slit also as it is not very distant from the previous slit , hence , you can assume the maximas and minimas of the new slit are located at same positions as of the previous slit .

So intensity will get 4 times at each place , but distribution will remain same .

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But won't it simply be a superposition of 2 single slit diffraction patterns? – Robin Thuran Malhotra Apr 23 '13 at 18:23
No , since both slits are a combination of many synchronised double slits . – user23503 Apr 27 '13 at 11:12

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