∵ Light is reflected twice by denser medium (first at air – oil in terface and then at oil – waterinterface), ∴ Δxnet = 2µoilt = nλ (for maxima) , for tmin n = 1 ⇒ t = 2 × 10−7 m If area of oil film = a, then 1m3 = at ⇒ 5 × 106m2 = 5km2
