A) 60 cm
B) 30 cm
C) 90 cm
D) 40 cm
Correct Answer: B
Solution :
\[P=0={{P}_{1}}+{{P}_{2}}-d\,{{P}_{1}}\,{{P}_{2}}\] \[\Rightarrow \,\,\,\,\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{d}{{{f}_{1}}{{f}_{2}}}\] \[\Rightarrow \,\,\,\,\frac{1}{10}+\frac{1}{20}=\frac{d}{10\,\,\times \,\,20}\] \[\Rightarrow \,\,\,\frac{30}{10\,\,\times \,\,20}\,\,=\,\,\frac{d}{10\,\,\times \,\,20}\] \[d\text{ }=\text{ }30\]You need to login to perform this action.
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