A concave lens of focal length 20 cm product an image half in size of the real object. The distance of the real object is

Question

A concave lens of focal length 20 cm product an image half in size of the real object. The distance of the real object is (A) 20cm (B) 30cm (C) 10cm (D) 60cm

Tardigrade Admin · Accepted Answer

We know that m=(f/f + u) (1/2)=(- 20/- 20 + u) or-20+u=-40 Or u=-40+20 or u=-20 cm

Q. A concave lens of focal length $20 c m$ product an image half in size of the real object. The distance of the real object is

$20 c m$

$30 c m$

$10 c m$

$60 c m$

We know that
$m = \frac{f}{f + u}$
$\frac{1}{2} = \frac{- 20}{- 20 + u} or - 20 + u = - 40$
Or $u = - 40 + 20$ or $u = - 20 c m$

Q. A concave lens of focal length 20cm product an image half in size of the real object. The distance of the real object is

20cm

30cm

10cm

60cm