A) 15 cm (concave)
B) 15 cm (convex)
C) 10 cm
D) 0
Correct Answer: A
Solution :
A concave lens is required by the person so that the lens forms the image of object distant 30 cm, at 10 cm it means \[u=-30\text{ }cm,\text{ }v=-10\text{ }cm\] \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] \[=\frac{1}{-10}-\frac{1}{-30}\] \[=-\frac{2}{30}\] Or \[\frac{1}{f}=\frac{-1}{15}\] So, \[f=-15cm\] Minus sign signifies that lens used is concave.You need to login to perform this action.
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