\(\frac{1}{v}\,\, - \,\,\frac{1}{{( - 2000)}}\,\,\, = \,\,\frac{1}{{0.5}}\,\,\)

\( \Rightarrow \,\,\,\frac{1}{v}\,\, = \,\,\frac{1}{{0.5}}\,\, - \,\,\,\frac{1}{{2000}}\,\, \cong \,\,\,\frac{1}{{0.5}}\,\,\left[ {as\,\,\,\frac{1}{{0.5}}\,\, >  > \,\,\,\frac{1}{{2000}}} \right]\,\,\,\)

\(v\,\, = \,\,\,0.5\,\,m\,\, = \,\,50\,\,cm\,\, = \,\,\,{{f}}\)

હેવ ,લેન્સ ના કિસ્સામાં,\(\,m\,\, = \,\,\,\frac{v}{u}\,\, = \,\,\frac{{0.5}}{{ - 2000}}\,\, = \,\,\, - \frac{1}{4}\,\, \times \,\,\,{10^{ - 3}}\)

તેથી,\({I_1} = \,\,(ma)\,\,(mb)\,\, = \,\,{m^2}A\,\,\,\,\,\,[\because \,\,\,A\,\, = \,\,\,ab]\,\,\,\,\,\)

\(i.e.,\,\,\,A\,\, = \,\,\frac{{{I_1}}}{{{m^2}}}\,\, = \,\,\,\frac{{18cm\,\, \times \,\,\,18cm}}{{{{\left[ {(1/4)\,\, \times \,\,\,{{10}^{ - 3}}} \right]}^2}}}\,\, = \,\,\,(720\,m\,\,\, \times \,\,\,720\,\,m)\)