S1 , S2  are two coherent sources of light. P is a point on the screen such that (S2P−S1P)=0.00897 cm . Wavelength of light used is 6000 A0 .  The order of the fringe formed at P is

Path difference x=0.00897 cm=897×10−7 m Wavelength λ=6000 A0=6000×10−10 m Path difference x=(2n−1)λ2          ⇒897×10−7=(2n−1)λ2          ⇒897×10−7 =(2n−1)6×10−72          ⇒2n−1=299          ⇒2n=300  ∴  n=150 dark