The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is cm.

Question

The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is cm. (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

m =( f / u + f ) + m =( f /-10+ f ) ⋅s (1) - m =( f /-20+ f ) ldots (2) (1) /(2) -1=( f -20/ f -10) 10- f = f -20 30=2 f f =15 cm

Q. The same size images are formed by a convex lens when the object is placed at $20 c m$ or at $10 c m$ from the lens. The focal length of convex lens is ___ $c m$ .

$m = \frac{f}{u + f}$
$+ m = \frac{f}{- 10 + f} \dots (1)$
$- m = \frac{f}{- 20 + f} \dots (2)$
(1) $/ (2)$
$- 1 = \frac{f - 20}{f - 10}$
$10 - f = f - 20$
$30 = 2 f$
$f = 15 c m$

Q. The same size images are formed by a convex lens when the object is placed at 20cm or at 10cm from the lens. The focal length of convex lens is ___cm.

m=u+ff​ +m=−10+ff​⋯(1) −m=−20+ff​…(2) (1) /(2) −1=f−10f−20​ 10−f=f−20 30=2f f=15cm

Q. The same size images are formed by a convex lens when the object is placed at $20 c m$ or at $10 c m$ from the lens. The focal length of convex lens is ___ $c m$ .

$m = \frac{f}{u + f}$
$+ m = \frac{f}{- 10 + f} \dots (1)$
$- m = \frac{f}{- 20 + f} \dots (2)$
(1) $/ (2)$
$- 1 = \frac{f - 20}{f - 10}$
$10 - f = f - 20$
$30 = 2 f$
$f = 15 c m$