A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observe on screen 1 m away. It is observed that the first minimum is at a distance of `2.5 mm` from the centre of the screen. Find the width of the slit.

Explanation

Given `lambda = 500 nm = 500 xx 10^(-9) m, D = 1m`,
`y_1 = 2.5 mm = 2.5 xx 10^(-3) m`
For first order minimum
`(y_1)/D = lambda/a`
or, `" " a = (lambda D)/(y_1) = (500 xx 10^(-9) xx 1)/(2.5 xx 10^(-3)) `
`= 200 xx 10^(-6)m = 2 xx 10^(-4) m = 0.2 mm`