A plane wavefront \[(\lambda =6\times {{10}^{-7}}m)\] falls on a slit \[0.4\,mm\] wide. A convex lens of focal length \[0.8\,m\] placed behind the slit focusses the light on a screen. What is the linear diameter of second maximum [RPMT 2001]

• A.            \[6\,mm\]                             
• B.            \[12\,mm\]
• C.            \[3\,mm\]                             
• D.            \[9\,mm\]