Question

a person with defective vision can see things clearly when they are up to distance 1 m only. find the nature focal length and power of the lens he will need to see a star clearly

Answer 1

Dear Student ,
Here in this case ,
$$\begin{gathered} \frac{1}{100}-\frac{1}{\infty }=\frac{1}{f} \\ \Rightarrow \frac{1}{f}=\frac{1}{100} \\ \Rightarrow f=100cm=1m \\ Sothelenswillbeconcavelens. \\ Powerofthelens=\frac{-1}{1}=-1D \end{gathered}$$
Regards