A plane wavefront `(lambda=6xx10^-7m)` falls on a slit `0.4m` wide. A convex lens of focal length `0.8m` placed behind the slit focuses the light on a screen. What is the linear diameter of second maximum?

Answer

`2.4 mm ; 6.0 mm`

Explanation

Here, `lambda = 6 xx 10^(-7)m, a = 0.4 mm = 4 xx 10^(-4)m`
`f = 0.8 m`
(i) Linear diameter of 1st minimum ,brgt `= 2x = (2 lambda f)/(a) = (2 xx 6 xx 10^(-7) xx 0.8)/(4 xx 10^(-4))`
`= 2.4 xx 10^(-3)m = 2.4 mm`
(ii) Linear diameter of second maximum, `(n = 2)`
`2x' = (2(2n + 1)lambda f)/(2a) = (2 xx 5 xx 6 xx 10^(-7) xx 0.8)/(2 xx 4 xx 10^(-4))`
`= 6 xx 10^(-3)m = 6.0 mm`