A) \[37.5cm\]
B) \[100.4cm\]
C) \[25.6cm\]
D) \[75.2cm\]
Correct Answer: A
Solution :
: The distance of normal vision is 25 cm. So if a book to be read is at \[m=-25cm\], its image should be formed at \[v=-75cm\]. Therefore, the required focal length (f) is \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] \[=\frac{1}{-75cm}-\frac{1}{-25cm}\] \[=\frac{-1}{75cm}+\frac{1}{25cm}=\frac{-1+3}{75cm}=\frac{2}{75cm}\] \[f=\frac{75cm}{2}=37.5cm\]
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