Question

A parallel beam of light of `600 nm` falls on a narrow slit and the resulting diffraction pattern is observed on a screen `.12 m` away. It is observed that the first minimum is at a distance of `3 mm` from the centre of the screen. Calculate the width of the slit.

Answer 1

Here, `lambda = 5000 Å = 600 nm = 6 xx 10^(-7)m`,
`D = 1.2 m, n = 1, x = 3 mm = 3 xx 10^(-3) m, a = ?`
For first minimum, `a sin theta = n lambda`
`a. ((x)/(D)) = 1 lambda`
`a = (lambda D)/(x) = (6 xx 10^(-7) xx 1.2)/(3 xx 10^(-3)) = 2.4 xx 10^(-4)m = 0.24 mm`