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 \[u=-\,30\,cm,\,\]\[\upsilon =-10\,cm\] \[\frac{1}{f}=\frac{1}{\upsilon }-\frac{1}{u}\] \[=\frac{1}{-10}-\frac{1}{-\,30}\] \[=-\frac{2}{30}\] or \[\frac{1}{f}=\frac{-1}{15}\] so \[f=-15\,cm\] Minus sign signifies that lens used is concaveYou need to login to perform this action.
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