A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance ?

Question

A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance ? (A) 36 cm (B) 25 cm (C) 30 cm (D) 150 cm

Tardigrade Admin · Accepted Answer

We have a lens of focal length 30 cm that produces 5 times magnified real image. So, we have (1/5 u)-((1/-u))=(1/30) Hence, (1/5 u)+(1/u)=(5+1/5 u)=(1/30) So, u=36 cm

Q. A convex lens of focal length $30 c m$ produces $5$ times magnified real image of an object. What is the object distance ?

$36 c m$

$25 c m$

$30 c m$

$150 c m$

We have a lens of focal length $30 c m$ that produces $5$ times magnified real image. So, we have
$\frac{1}{5 u} - (\frac{1}{- u}) = \frac{1}{30}$
Hence, $\frac{1}{5 u} + \frac{1}{u} = \frac{5 + 1}{5 u} = \frac{1}{30}$
So, $u = 36 c m$

Q. A convex lens of focal length 30cm produces 5 times magnified real image of an object. What is the object distance ?

36cm

25cm

30cm

150cm