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A lens forms a real image of an object. The distance from the object to the lens is * u * cm and distance of the image from the lens is *v* cm. The given graphs shows variation of *v * with

(i) What is the nature of the lens?

(ii) Using the graph, find the focal length of this lens.

$Fromthegraph,whenu=20cm,wehavev=20cm.\phantom{\rule{0ex}{0ex}}Fortheconvexlensformingarealiamge,uisnegativeandvandfarepositive.\phantom{\rule{0ex}{0ex}}u=-20cmandv=+20cm\phantom{\rule{0ex}{0ex}}U\mathrm{sin}gthislensformula,\phantom{\rule{0ex}{0ex}}\frac{1}{f}=\frac{1}{v}\u2013\frac{1}{u}=\frac{1}{20}\u2013\frac{1}{-20}=\frac{1}{10}\phantom{\rule{0ex}{0ex}}\Rightarrow f=+10cm$

Regards

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