Question

The distance between an object and its upright image is `20 cm.` if the magnification is `0.5,` what is the focal length of the lens that is being used to form the image?

Answer 1

Correct Answer - C::D
Diminished erect image is formed by concave lens.
Let `u=-x,` then `v=-x/2`
Now, `|u|-|v|=20 cm`
`:. x/2=20 cm or x=40 cm`
`:. u=-40 cm and v=-20 cm`
`1/f=1/-20-1/-40`
or `f=-40 cm`