The angular fringe width is given by \(\alpha=\frac{\lambda}{ d }\) where \(\lambda\) is wavelength and \(d\) is the distance between two coherent sources. Thus \(d =\frac{\lambda}{\alpha}\)

Given, \(\lambda=6280 \mathring A, \alpha=1^{\circ}=\frac{\pi}{180}\) radian .

\(d =\frac{6280 \times 10^{-10}}{3.14} \times 180\)

\(=3.6 \times 10^{-5}\,m =0.036\,mm\)