A) 15 cm (concave)
B) 15 cm (convex)
C) 10 cm
D) 0
Correct Answer: A
Solution :
Since, the person is not able to see distant objects beyond 10 cm so, he should use concave lens in his spectacles. Concave lens will form the image of object distant 30 cm, at 10 cm it means \[u=-30\text{ }cm,\text{ }v=-10\text{ }cm\] \[\frac{1}{f}=\frac{1}{\upsilon }-\frac{1}{u}\] \[=\frac{1}{-10}-\frac{1}{-30}\] \[=-\frac{2}{30}\] Or \[\frac{1}{f}=-\frac{1}{15}\] So, \[f=-15cm\] Minus sign signifies that lens used is concaveYou need to login to perform this action.
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