Question

An object 6.0 c.m. tall is placed on the principal axis of convex lens . It's 3.0c.m. tall image is formed on the screen placed at a distance of 30 cm from the lens , the focal length of the lens is​

Answer 1

We know that,

Magnification m=- v/u=h'/h=30/20

and also v=10cm

So u=-20/3 cm

Using formula,

1/v -1/u=1/f

1/10 + 1/(20/3)=1/f

or f=4 cm

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