Question

A convex lens of focal length 40 cm . Calculate distance at which object should be placed from lens so that it forms an image at 60 cm on the other side of the lens. Find magnification

Answer 1

Dear Student
$$\begin{gathered} f=+40cm \\ v=+60cm \\ \frac{1}{f}=\frac{1}{v}-\frac{1}{u} \\ \frac{1}{u}=\frac{1}{v}-\frac{1}{f}=\frac{1}{60}-\frac{1}{40}=\frac{40-60}{60\times 40}=-\frac{20}{60\times 40} \\ u=-120cm \\ m=\frac{h_2}{h_1}=\frac{v}{u}=\frac{60}{-120}=-\frac{1}{2} \\ Negativesignofmindicatesthatimageisinverted. \end{gathered}$$
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