Question

In Fraunhofer diffraction, how is the angular width of the central bright fringe affected when slit separation is increased?

Answer 1

In Fraunhofer diffraction, $b\sin \theta =n\lambda$
where $b$ is the width of slit, $\lambda$ is the wavelength of light used.
For central bright fringe, $n=1$
$⟹b\sin \theta =\lambda$
Thus angular width of central bright width $=2\sin \theta =\frac{2\lambda }{b}$
So, angular width of central bright fringe will decrease when the width of slit is increased.