c
પ્રકાશિત શલાકા માટે સંપાતબિંદુ પાસે પથ-તફાવત 

 \(\frac{{{\text{xd}}}}{{\text{D}}}\,\, = \,\,n\lambda \)પરથી \(\,\,{\lambda _1}\, = \,\,\,590\,\, \times \,\,{10^{ - 9}}\,\,m,\,\,{n_1}\,\, = \,\,3\,,\,\,{\lambda _2}\,\, = \,\,?,\,\,{n_2}\,\, = \,\,4\)

\({n_1}{\lambda _1}\,\, = \,\,{n_2}{\lambda _2}\,\,\therefore \,\,{\lambda _2}\,\, = \,\,\frac{{{n_1}{\lambda _2}}}{{{n_2}}}\,\)

\( = \,\,\frac{{3\,\, \times \,\,590\,\, \times \,\,{{10}^{ - 9}}}}{4}\,\, = \,\,442.5\,\,nm\)