where \(b\) is slit width.

In Young's double slit experiment, angular width of each fringe is \(\frac{\lambda}{d}\)

where \(d\) is the distance between the two slits.

Given: \(d=6.1 b\) So, number of maximas observed in central maxima of diffraction pattern \(n=\frac{2 \lambda}{\frac{b}{\lambda}}\)

\(\therefore n=\frac{2 d}{b}=2 \times 6.1=12.2\)

Thus 12 maximas are observed.