Two identical coherent sources are placed on a diameter of a circle of radius R at separation x(<

Path difference at P isΔx=2(x2cosθ)=xcosθ for intensity to be maximumΔx=nλ     (n=0,1,2,3,........)Or cosθ=nλx≥1∴n≥xλSubstituting x=5λ , we getn≥5 or n=1,2,3,4,5,........Therefore, in all four quadrants there can be 20 maxima. These are more maxima at θ=00 andθ=1800 . But n=5 corresponds to θ=900 and θ=2700 which are coming only twice while we have multiplied it four times. Therefore total number of maxima is still 20. I.e. n=1 to 4 in four quadrants (total) 16 plus more at θ=00,900,1800 and 2700 .