a
હવામાં \(\frac{1}{{{{f}_a}}}\,\, = \,\,{(_a}{\mu _g} - 1)\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\)

\( = \,\,(1.5 - 1)\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\,\,\, = \,\,(0.5)\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\,\,........\,\,\,(1)\)

પ્રવાહી  \(\frac{1}{{{{f}_{l}}}}\,\,\, = \,\,\,{(_{l}}{\mu _g} - 1)\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\,\,\,\,\, \Rightarrow \,\,\,\,\,\frac{1}{{{{f}_{l}}}}\,\, = \,\,\,\left( {\frac{{1.5\,\, - \,\,1.6}}{{1.6}}} \right)\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\)

\( = \,\, - \,\,\,\frac{{0.1}}{{1.6}}\,\,\,\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\,\,\,..........\,\,\,(2)\)

\((1)\) અને \((2)\) ને \(\mu\) વડેભાગતા  \(\frac{{{{f}_{l}}}}{{{{f}_a}}}\,\, = \,\,\, - 8\,\,\,\, \Rightarrow \,\,\,{{f}_{l}}\,\, = \,\, - 8\,\,{{f}_a}\)

પરંતુ હવામાં લેન્સનો ઓપ્ટિકલ પાવર \( - 5D\)  છે તેથી \(\,{{f}_a} = \,\,\, - \frac{{100}}{5}\,\,\,cm\,\,\, = \,\, - 20\,\,\,cm\)

\({{f}_{l}} = \,\, - 8\,\, \times \,\,( - 20)\,\,\, = \,\,160\,\,cm\)   અથવા \(\,1.6\,\,m\,\,\,\,\)

અને પ્રવાહી માધ્યમમાં લેન્સનો પવાર \({P_{l}}\, = \,\,\frac{\mu }{{{f_\ell }}}\,\, = \,\,\frac{{1.6}}{{1.6}}\,\, = \,\, + \,\,1D\)