Question

A concave lens of focal length of 25 cm . At what distance should the object from the lens be placed so that it forms an image at 20 cm distance from the lens . Also find the magnification produced by lens

Answer 1

Dear Student,
$$\begin{gathered} letimagedis\tan ceisu \\ herev=20cm \\ then \\ \frac{1}{20}-\frac{1}{u}=\frac{1}{-25} \\ u=\frac{20\times 25}{20+25}=\frac{500}{45}=\frac{100}{9}cm \\ andmagnification=\frac{v}{u}=\frac{20\times 9}{100}=\frac{9}{5}=1.8 \end{gathered}$$
Regards