devarshi-dt-logo

Question:

A short liner object, of length l, lies along the axis of a concave mirror, of focal length f, at a distance d from the pole of the mirror. The size of the image is then (nearly):

lfd−f

lf2(d−f)2

(d−f)2f2l

d−fIf

Solution:

From mirror equation, 1/v + 1/u = 1/f ⟹ |dv| = ||v²/u²|| |du|
|dv| is the size of image
|du| is the size of object
From the equation v²/u² = v²/d² = (fd/(d−f))²
Thus size of the image is lf2(d−f)2