CBSE Class 10 Science 2017 · Paper 31/1/2 · Question 4

With $u=-40$ cm and $f=R/2=+20$ cm, the mirror formula gives $\frac{1}{v}=\frac{1}{20}+\frac{1}{40}=\frac{3}{40}$, so $v=+\frac{40}{3}$ cm $\approx +13.3$ cm, and $m=-\frac{v}{u}=+\frac{1}{3}$. The four characteristics of the image are: (1) Virtual: it is formed behind the mirror and cannot be obtained on a screen. (2) Erect: $m$ is positive. (3) Diminished: it is one-third the size of the object. (4) Position: $13.3$ cm behind the mirror, between the pole and the principal focus.