Light – Reflection and Refraction: CBSE Class 10 Physics practice questions

C. It is real and inverted

A plane mirror forms an image that is virtual and erect, equal in size to the object and as far behind the mirror as the object is in front. It is also laterally inverted (left and right swap). Saying the image is real and inverted is wrong: the rays only appear to come from behind the mirror, so no screen can show it.

B. 2 m

After walking 1 m she is 1 m from the mirror. Her image is also 1 m behind the mirror, so the gap between her and her image is $1 + 1 = 2\ \text{m}$. Traps: 4 m is the separation before she moved, 3 m comes from adding the 1 m walk to 2 m, and 1 m is only her distance from the mirror.

C. +1.15 m, behind the mirror

Here $f = \dfrac{R}{2} = +1.50\ \text{m}$ and $u = -5.00\ \text{m}$. So $\dfrac{1}{v} = \dfrac{1}{f}-\dfrac{1}{u} = \dfrac{1}{1.50}+\dfrac{1}{5.00} = 0.867$, giving $v = +1.15\ \text{m}$ (behind the mirror, virtual). Traps: 2.14 m uses $u = +5$, 1.88 m uses $f = R = 3$, and $-1.15$ m is a sign slip. The magnification is $m = -v/u = +0.23$ (erect, diminished).