Question

A `5.0` cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. By calculation, determine (i) the position (ii) the size of the image formed.

Answer 1

Here, `h_(1)= 5.0cm, f=20cm,u = -30 cm,v=?, h_(2)=?`
From `(1)/(v) - 1/u =(1)/(f), (1)/(v) = (1)/(f) + 1/u = 1/20 - 1/30 =(3-2)/(60) =1/60` or `v=60cm`.
`:.` image is formed on the other side of the lens at 60 cm from the lens.
From `(h_(2))/(h_(1)) =v/u, h_(2) =v/u xx h_(1)=60/-30 xx 5.0 = -10cm`
Negative sign shows that image is inverted and real. Its size is 10cm.