Explanation

(c) For a slit of width $a,$ light of wavelength $\lambda,$ when light falls on the slit, the diffraction patterns so obtained as
[image:10_image25.emf]
The first diffraction minimum occurs at the angles given by
$\sin\theta = \frac{\lambda}{a}$
From the equation, it is clear that width of the central diffraction maximum is inversely proportional to the width of the slit. On increasing the width size$a$, the angle $\theta$ at which the intensity first becomes zero decreases, resulting in a narrower central band and if the slit width is made smaller, the angle $\theta$ increases, giving a wider central band.