JEE Main · 2021 · 26 Feb 2021 · Shift 1 · Geometrical Optics

The image keeps the orientation of the object and is one quarter as tall, so the magnification is $m=+0.25$. A single mirror gives an erect image only when that image is virtual, and a virtual image lies behind the mirror, on the side opposite the object. A concave mirror forms a virtual image only for an object closer than its focus, and such an image is always larger than the object, so it cannot have $m=0.25$. A convex mirror always forms a virtual, erect and diminished image, and $m=\frac{f}{f-u}$ with $f=+40$ cm and $u=-120$ cm gives $m=\frac{40}{160}=0.25$, a consistent object position. The mirror is convex and the image is virtual, lying on the side of the mirror opposite the object.