Each light source $\left({\mathrm{S}}_1,{\mathrm{S}}_2,{\mathrm{S}}_3,{\mathrm{S}}_4,{\mathrm{S}}_5,{\mathrm{S}}_6\right)$ in a line has same power, same wavelength $\left(\lambda \right)$and all are in phase. Distance between consecutive sources is a if smallest value of a is a’ such that point P(r> > a) has zero light intensity, find the value of ${\left(\frac{\lambda }{a^{\mathrm{\prime }}}\right)}^2$