The distance between object and its 3 times magnified virtual image as produced by a convex lens is 20cm . The focal length of the lens used is ________ cm .

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The distance between object and its 3 times magnified virtual image as produced by a convex lens is 20cm . The focal

The image will be formed on the same side as the object. Therefore, $v = 3u$

Given: \left|v – u\right| = 20cm $$ ⇒ \left|2u\right| = 20cm $$ ⇒ u = - 10cm $(-ve sign as the object is real)From lens formula, we can write $ \dfrac{1}{( - 30 )} - \dfrac{1}{( - 10 )} = \dfrac{1}{f} $$ ⇒ f = 15cm

The distance between object and its 3 times magnified virtual image...

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