A) - 2.5 D and concave lens
B) - 2.5 D and convex lens
C) - 3.5 D and concave lens
D) - 3.5 D and convex lens
Correct Answer: A
Solution :
\[u=\infty ,\,\,v=-40m\] \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] \[\frac{1}{f}=\frac{1}{-40}-\frac{1}{\infty }\] \[\frac{1}{f}=\frac{1}{-40}\] Power \[P=\frac{1}{f}=-\frac{1}{40}\] \[=-2.5D\] Negative sign shown s that lens used is concave lens.
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