Question
In a diffraction pattern due to single slit of width a, the first minimum is obsrved at an angle 30o when light of wavelength 
is incident on the slit. The first secondary maximum is observed at an angle of:
-
sin-1 (2/3)
-
sin-1 (1/2)
-
sin-1 (3/4)
-
sin-1 (1/4)
Solution
C.
sin-1 (3/4)
Given that, first minimum is observed at an angle of 30o in a diffraction pattern due to a single slit of width a.
i.e., n =1, 
According to the Bragg's law of diffraction,
For 1st secondary maxima,
... (2)
Putting the value of a from Eqn. (i) to Eqn. (ii), we get
