Question

Find the position, nature and size of the image formed by a convex lens of focal length 20 cm of an object 4 cm high placed at a distance of 30cm from it.

Answer 1

Here, `v=? h_(2) =?,f=20cm,h_(1)=4cm,u= -30cm`
As `(1)/(v) - 1/u = (1)/(f), :. (1)/(v) = (1)/(f) + 1/u =1/20 - 1/30 = (3-2)/(60) =1/60`
`v =60 cm`
As v is positive, the image is real, formed on the right side of the lens.
Also, `m= (h_(2))/(h_(1))=v/u, :. h_(2)/4= 60/-30 = -2`
`h_(2) = -8 cm`
Negative sign of `h_(2)` indicates that the image is inverted.