In a Young’s double slit experiment, the ratio of amplitude...

The ratio of the maximum to minimum intensity is given by

\dfrac{{I}_\max}{{I}_\min} = \dfrac{{\left(\sqrt{{I}_{1}} + \sqrt{{I}_{2}}\right)}^{2}}{{\left(\sqrt{{I}_{1}} - \sqrt{{I}_{2}}\right)}^{2}}

It is given that $\dfrac{{A}_{1}}{{A}_{2}} = \dfrac{2}{1}$

\dfrac{{I}_\max}{{I}_\min} = {\left(\dfrac{{A}_{1} + {A}_{2}}{{A}_{1} - {A}_{2}}\right)}^{2} = \dfrac{{A}^{2}2{\left(2 + 1\right)}^{2}}{{A}^{2}2 ( 2 - 1{)}^{2}} = {\left(\dfrac{2 + 1}{2 - 1}\right)}^{2} = \dfrac{9}{1}