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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.

Answer» Here, `lambda = 500 nm = 500 xx 10^(-9)m = 5 xx 10^(-7)m, D = 1m, n = 1, x = 2.5 mm = 2.5 xx 10^(-3)m, a = ?`
The condition for minima is `a(x)/(D) = n lambda`
`a = (n lambda D)/(x) = (1 xx 5 xx 10^(-7) xx 1)/(2.5 xx 10^(-3)) = 2 xx 10^(-4)m = 0.2 mm`


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