Question

A concave lens has focal length of 15 cm. At what distance should
the object from the lens be placed so that it forms an image at 10 cm
from the lens? Also, find the magnification produced by the lens.​

Answer 1

QuesTion :-

A concave lens has focal length of 15 cm. At what distance should  the object from the lens be placed so that it forms an image at 10 cm  from the lens? Also, find the magnification produced by the lens.​

SoluTion :-

$\boxed {\rm {\frac{1}{v}-\frac{1}{u} =\frac{1}{f}}}$

⇒ V is negative.

⇒ Focal Length is negative.

$\sf {-\frac{1}{10} -\frac{1}{u} =-\frac{1}{15}}\\\\\\\sf {-\frac{1}{u} =-\frac{1}{15} +\frac{1}{10}}\\\\\\\sf {\frac{1}{u} =\frac{-10+15}{150}}\\\\\\\sf {\frac{1}{u} =\frac{5}{150} }\\\\\\\sf {\frac{1}{u} =\frac{1}{30}}\\\\\\\sf {u=-30 \ cm}$

Now,

$\rm {Magnification = -\frac{v}{u} }\\\\\\\rm {M=\frac{-10}{-30}}\\\\\\\rm {M=\frac{1}{3}}$

Answer 2

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