# Let's see the path

**Classical Mechanics**Level 5

Two mirrors \(M_1\) and \(M_2\) make an angle \(\phi\) with line \(AB\). A point source \(S\) is kept at a distance r from the point of intersection of mirrors. A small hemispherical annular mask is kept close to \(S\) so that no ray emanating from \(S\) directly reaches the screen kept at a distance \(b\) from the source. Interference pattern of rays reflected from \(M_1\) and \(M_2\) is observed on the screen. The fringe width of this interference pattern is (in **micro-meter** )

\(\lambda=5000 \mathring { A } \), \(b=4~m\), \(r=1~m\), \(\phi=30^{\circ}\)