Question

The distance between an object and a screen is 49 cm. A convex lens is placed between the object and the screen so as to get an image on the screen magnified six times. calculate the focal length of the lens.​

Answer 1

Answer:

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Explanation:

Answer 2

Answer:

The focal length of the lens is 6cm.

Explanation:

Given the magnification, $\frac{v}{u} =6\implies v=6u$

          distance between an object and a screen,

                     $u+v= 49 cm$

                   $u+6u= 49 \implies 7u=49$

   Therefore, object distance, $u=\frac{49}{7} =7cm$

Then from $u+v= 49 \implies 7+v=49$

   Therefore, image distance, $v=42cm$

   focal length of the lens, $\frac{1}{f} =\frac{1}{u}+\frac{1}{v}$

                                         $\frac{1}{f} =\frac{1}{7}+\frac{1}{42}=\frac{6+1}{42} =\frac{7}{42}=\frac{1}{6}$

Therefore, the focal length of the lens is 6cm.