In Young's experiment, find the distance between two slits that results in the third minimum for `420 nm` violet light at an angle `30^(@)`
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Explanation

`S_(2) L = d sin theta`
or `Delta x = d sin theta`
For intensity to be minimum,
`Delta x = sin theta`
`Delta x = (2n - 1) lambda // 2`
`n = 1, 2, 3,…`
For third minimum, `n = 3`
`d sin theta = (5 lambda)/(2)`
Given: `lambda = 420 nm = 420 xx 10^(-9) m`
`theta = 30^(@)`
`:. d sin 30^(@) = (5)/(2) xx 420 xx 10^(-9) implies d = 2.1 xx 10^(-6) m`.