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Similarly to the previous part, we have a source of waves. We still have two slits and in the end there is another detector which counts the energy of each wave which reaches it.
The curve represents the energy of the waves reaching the detector is the curve Ι. The curve Ι12 represents the energy detected whan both slits remain open. It is quite different from the curve N12 which was detected in the previous part of the experiments. However it is normal to take such a curve since waves act different than particles and they interfere with each other their own way.
Similarly to the previous part the curve Ι1 is the result of the experiment when the slit No2 has been removed and the curve Ι2 is the one when slit No1 has been removed. Have a look at the curves Ι1 and Ι2: they are alike to the curves N1 and N2 of the previous part, but the curve Ι12 is not the same as the curve N12.
The height h of the water behind the slits is equal to the height when the slit No1 is open plus the height when the slit No2 is open. In other words there is interference for the heights of the water. The energy of each wave is proportional to the square if the height.
h12=h1+h2
but Ι12 not equal to Ι1+Ι2
I12~(h12)2
I1~(h1)2
I2~(h2)2