A) 45 dioptres
B) 9 dioptres
C) 1/9 dioptre
D) 6 dioptres
Correct Answer: B
Solution :
\[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{20}+\frac{1}{25}\]\[\Rightarrow \]\[F=\frac{100}{9}\]\[cm=\frac{1}{9}\]\[metre\] \[\therefore \] \[P=\frac{1}{1/9}D=9D\]You need to login to perform this action.
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