Two spectral lines of sodium D1 and D2 have wavelengths of approximately 5890 and 5896 sodium lamp sends incident plane wave on a slit of width 2 x 106 m. A screen is located 2 m from the slit. Find the spacing between the first maxima of two sodium lines as measured on the screen.
The distance of first secondary maxima from the centre of screen,
∴ Spacing between the first maxima for D1 and D2 lines
= 0.8844 - 0.8835
= 9 x 10-4 m = 0.9 mm
