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Asked in GUJCET 2026 · Mirror formula and magnification
Given: concave mirror with f=15 cm, object 10 cm in front, so u=-10 cm and f=-15 cm.
Idea: the object lies inside the focal length, so work out v from 1/v+1/u=1/f and read off the sign.
1/v=1/(-15)-1/(-10)=(-2+3)/(30)=1/(30)
v=+30 cm, positive, so the image lies behind the mirror and is virtual.
m=-v/u=-(30)/(-10)=+3, positive and greater than one, so it is erect and three times as large.
This is the shaving-mirror case: hold your face inside the focus of a concave mirror and you see an upright, enlarged image.
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