A source emitting light of wavelengths 480 nm and 600 nm is used in a double slit interference experiment. The separation between the slits is 0.25 mm and the interference is observed on a screen placed at 150 cm from the slits. Find the linear separation between the first maximum (next to the central maximum) corresponding to the two wavelengths.

We know that, the first maximum (next to central maximum) occurs at y = λD/d Given that, λ base 1 = 480 nm, λ base 2 = 600 nm, D = 150 cm 1.5 m and d = 0.25 mm = 0.25 * 10^-3 So, y base 1 = Dλ base 1/d = 1.5 * 480 * 10^-9/0.25 * 10^-3 = 2.88 mm Y base 2 = 1.5 * 600 * 10^-9/0.25 * 10^-3 = 3.6 mm. So, the separation between these two bright fringes is given by, ∴ separation = y base 2 – y base 1 = 3.60 – 2.88 = 0.72 mm.