Question

in a convex lens an image is formed which is 3 times greater than the object .if the focal length of the lens is 25 CM then fine the position of the object.

Answer 1

HEY!!

Here f= 25 cm (positive for convex lens)

m(magnification )=-3 (as image is real it will be inverted)

m=-(V/U)

-3=-V/U

V=3U

using lens formula =>1/V-1/U=1/f
1/3U-1/U=1/f
1/U-3/U=1/25
-2/U=1/25
-2×25=U
-50cm=U
V=3U
V=3×-50
V=-150 cm
HOPE IT HELPS YOU..

Answer 2

The object is placed at a distance of 16.7 cm.

Explanation:

Given that,

The formed image by a convex lens is 3 times greater than the object, magnification of the lens is 3. Magnification is given by :

$m=\dfrac{v}{u}\\\\v=mu\\\\v=3u.................(1)$

Focal length of the lens is 25 cm, f = +25 cm

We need to find the position of the object. It can be given by using lens formula as :

$\dfrac{1}{3u}-\dfrac{1}{u}=\dfrac{1}{25}\\\\u=-16.7\ cm$

Put u in equation (1)

$v=3\times (-16.7)\\\\v=-50.1\ cm$

So, the object is placed at a distance of 16.7 cm. Hence, this is the required solution.

Learn more,

Lens formula

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