Two radio frequency point sources S1  and S2 , separated by distance 2.5 m are emitting in phase waves of wavelength 1 m. A detector moves in a large circular path around the two sources in a plane containing them. The number of maxima that will be detected by it over the complete circular path, are

At point A, the path difference is 2.5λ and at B, path difference is zero. While moving from A to B , path difference changes from 2.5 to zero, making two maxima corresponding to 2 λ and λ  (excluding). B is common for both upper quarter circles hence there are five maxima in one half circle, making 10 in total circular movement.