Q.

In a diffraction pattern due to a single slit of width a, the first minimum is observed at an angle 30° when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observed at an angle of          [2016]
 

1 sin-1(12)  
2 sin-1(34)  
3 sin-1(14)  
4 sin-1(23)  

Ans.

(2)

For first minimum, the path difference between extreme waves, asinθ=λ

Here θ=30°sinθ=12  a=2λ                    ...(i)

For first secondary maximum, the path difference between extreme waves

asinθ'=32λ  or  (2λ)sinθ'=32λ  [Using eqn (i)]

or  sinθ'=34   θ'=sin-1(34)