A) 15 cm (concave)
B) 15 cm (convex)
C) 10cm
D) Zero
Correct Answer: A
Solution :
Key Idea: The defect of short-sightedness is removed by using a lens which diverges the rays from object. The person can see near object (10 cm) but cannot see the distant objects distinctly. In order to remove this defect a concave lens of suitable focal length is used which diverges the rays from a distant object reaching the eye such that they appear to be coming from the eye?s own far point\[P\]. From lens formula \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=-\frac{1}{10}-\left( -\frac{1}{30} \right)=-\frac{2}{30}\] \[\Rightarrow \] \[\frac{1}{f}=-\frac{1}{15}\] \[\Rightarrow \] \[f=-15\,\,cm\]You need to login to perform this action.
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