Question

A convex lens of focal length 16 cm forms a real image double the size of the object. The distance of the object from the lens is?

Answer 1

The object is placed at a distance of 8 cm from the lens.

Explanation:

Given that,

Focal length of a convex lens, f = +16 cm

The lens forms a real image double the size of the object, the magnification of the lens is 2.

To find,

The object distance.

Solution,

The magnification of a lens is given by :

$m=\dfrac{v}{u}$

$2=\dfrac{v}{u}$

v = 2u

Now using lens formula as :

$\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}$

$\dfrac{1}{2u}-\dfrac{1}{u}=\dfrac{1}{16}$

On solving the above equation, we get :

u = -8 cm

So, the object is placed at a distance of 8 cm from the lens.

Learn more,

Lens formula

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Answer 2

8 cm is the answer for the given question..