A) \[-1D\]
B) \[1D\]
C) \[-25\,D\]
D) \[25\,D\]
Correct Answer: B
Solution :
\[\frac{1}{{{f}_{a}}}=\left( \frac{1.5}{1}-1 \right)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] ....(i) \[\frac{1}{{{f}_{m}}}=\left( \frac{{{\mu }_{g}}}{{{\mu }_{m}}}-1 \right)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] \[\frac{1}{{{f}_{m}}}=\left( \frac{1.5}{1.6}-1 \right)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] ?.(ii) Dividing (i) by (ii), \[\frac{{{f}_{m}}}{{{f}_{a}}}=\left( \frac{1.5-1}{\frac{1.5}{1.6}-1} \right)=-8\] \[{{P}_{a}}=-5=\frac{1}{{{f}_{a}}}\Rightarrow {{f}_{a}}=-\frac{1}{5}\] \[\Rightarrow \,\,{{f}_{m}}=-8\times {{f}_{a}}=-8\times -\frac{1}{5}=\frac{8}{5}\] \[{{P}_{m}}=\frac{\mu }{{{f}_{m}}}=\frac{1.6}{8}\times 5=1D\]
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