CBSE Class 10 Science 2019 · Paper 31/3/1 · Question 19

(a) The image formed by a plane mirror is (1) virtual and erect - it cannot be obtained on a screen; (2) of the same size as the object; (3) as far behind the mirror as the object is in front of it; (4) laterally inverted. (b) With the sign convention, $h=+5$ cm, $u=-20$ cm, $f=-30$ cm. Mirror formula: $\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=-\frac{1}{30}+\frac{1}{20}=\frac{1}{60}$, so $v=+60$ cm: the image is formed $60$ cm behind the mirror. Magnification $m=-\frac{v}{u}=-\frac{60}{-20}=+3$, so $h^{\prime }=m\times h=3\times 5=+15$ cm. The image is $15$ cm tall - virtual, erect and enlarged (three times the size of the object).