Given data
wavelength λ=2.5 µm =2.5×10⁻⁶m
Diameter d=0.20 mm =0.20×10⁻³m
To find
Angle Θ in radians and degree
Solution
Circular apertures have first dark fringe at
Θ=(1.22λ)/d
Substitute the given values
So
Θ=[1.22(2.5×10⁻⁶m)]/0.20×10⁻³m
Θ=0.01525 rad
or
Θ=0.87°
And that’s why I think it might be C or D.
