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?


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 .

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

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