A) 15 cm (Concave)
B) 15 cm (Convex)
C) 10 cm
D) 0
Correct Answer: A
Solution :
[a] The person suffers from short-sightedness because he is unable to see objects at normal distance but can see objects at nearer distance. He will require concave lens. Things placed at 30 cm will appear to be placed at 10cm. So, u = 30; v = 10; f = ? From lens formula \[\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\] \[\Rightarrow \] \[-\frac{1}{10}+\frac{1}{30}=\frac{1}{f}\] \[\Rightarrow \] \[\frac{-3+1}{30}=\frac{1}{f}\] \[\Rightarrow \] \[f=-\frac{30}{2}=-15cm\] Negative sign indicates that lens used is concave.You need to login to perform this action.
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